There are different materials used in the construction of rigid foam insulation. The best is a double foil faced ISO poly variant. In a one inch panel, you will end up with an R value of ~ R5, which combined with the reflectivity of both sides, will insulate your dressing area quite well.

The next best is XPS expanded polystyrene, which is water proof, less expensive and has no foil facing. It has a similar R value, but no reflectivity. Both of these insulations are commonly found in the big box stores.

The area you are planning to heat or cool, is so small that any attempt to insulate will result in beneficial results, A small disc heater can easily heat the entire area, and a smaller AC unit can cool all but the larger ducted LQs.

One inch of insulation is all you need. Make sure to cover the ends of the wall studs as well. They conduct the heat and cold into the interior as easily as the outside skin.

Measure how deep your supports are in the living space. Buy the insulation boards that have blue on one side and foil on the other. Install according to the directions on the insulation panels. (whichever way the foil side goes. In mine, they are on the inside, with blue to the outside.)

Use the special metal tape (not duct tape) to attach the insulation to your steel supports. Once you put these insulation sheets in and decide on your furring strips to go over them, measure your furring strip thickness and buy more insulation, that thickness... if you want.  I didn't do the second layer of insulation because I cut all my own furring strips from larger dimension lumber and it wasn't worth it as my strips were less than 1/2 inch thick.

If you have a GN and will be sleeping up in that area... what I did was lay 2x4s flat which gave me 1 1/2" height to fill with insulation. There I used the pink styrofoam sheets, no foil. Then 3/8" plywood over the insulation and 2x4s. Was very easy to do that way with the tapered nose and angles. Unfortunately, it also took away vertical space... but... it's cold without insulation under your mattress!!

Another product that is helpful to have is the foil bubble wrap insulation. This can be cut to size and tucked into those places that are curved - around windows, between wall and ceiling, etc.  This is the most expensive of all the insulation types. I used a combination of this with the blue/foil insulation sheets. Just tape pieces together with the metal tape.

Several friends insulated their unfinished areas and still haven't done anything else (no wood paneling or anything).  We all use the Mr Heater, buddy heaters running on propane or small battery operated fans.

You can spend LOTS of money trying to have bragging rights for how well insulated your trailer is. Or you can forget the insulation and spend more money on the energy cost to heat or cool your trailer.  A LQ is not a large area, You only use it a few time a year vs your home that you are in 24x7. Sometimes trying to be too energy efficient will cost more the the amount of energy you will save. We do it all the time in the housing industry where folks want to brag about their $5 per month electric bill, but forget to tell their neighbors about the $20,000 they spent on extra insulation, triple paned windows.

There are 3 types of heat/cooling loss.

Inflitration

Conduction

Convection

Infiltration is usually the biggest heat loss. You open your door and cold air rushing in. If a strong wind is blowing you can almost have 100% air turn over in the 30 seconds the door is open. So we usually start with trying to seal up an area to stop outside air from moving thru or replacing the inside air.  Make sure that windows and doors seal tightly, that all cracks and penetrations are properly sealed.

Conduction is the movement of heat thru a wall by moving thru the materials,  Materials like Aluminum and Steel will move the heat/cold faster than low density materials like Foam or even dead air space. We usually address this problem by placing low density materials between the outer surface and the inner surface. Fiberglass insulation, foam board etc will slow the thermal transfer . Since we are dealing with a small area that has other thermal problems, we usually don't go to over board. 1/2" or 1" of insulation is usually adequet. Any more usually doesn't show any improvement in energy consumption.

Convection.  Dead air is a good insulator.  Problem is air doesn't stay motionless.  If you have thermal energy against the outside of horse trailer.  That energy transfers the metal skin into the dead air space.  The air temp next to the out wall changes and that air rises. The vaccume draws the air fromt he inner wall surface and we create circulation that moves the dead around around in what every space it is confined.  Hence we need to trap the dead air so it can't circulate. That is why Bubble wrap or products with high air entrapment make good insulators. They trap dead air in very small confined spaces where it can't move.  For your trailer, this means No large voids of dead.  Fill any spaces with something that stops air movement.   Putting an 1" of foamin a wall cavity can be totally useless if you leave a 1/2" gap between the foam and the stud.  Cold or heat will move via air convection and the foam you put in is wasted.  Cut your foam to fit tightly into any spaces you place it. A nice snug friction fit is better than small void.

One other issue is that heat can radiate.  Products will foil faces that relect heat back to where it came from can also be very usefull.   If I were insulating a trailer to stay cold and have better air conditioning, I would place the foil on the outside.  If I wanted to retain heat inside the trailer. I would place the foil facing in to reflect the heat back into the trailer.

Long story short.  The thickness of the insulation isn't near as important as sealing any holes or penetrations, making sure that all voids are filled so that the air will not circulate in the cavity and placing some type of insulation between the inner and outer surfaces.

painted horse,

    So with regards to the Sundowner I bought and asked about in the other thread.  If there are no beams to fit the insulation between, do I just try and glue them as close together as I can?  I am thinking I might insulate the roof first and leave the walls and see how it does.  I don't want to turn this into a fancy living courters, just want to camp in it and have a place to go at shows when it is really cold or hot.  Thanks

Having an inner panel already installed in your DR has some advantages, regardless if it's insulated or not.

It allows you to affix any number of appointments, without having to first install interior framing and worry about puncturing the exterior skin with fasteners.

It's an ideal surface on to  which to add insulation. A foil faced rigid foam board can be glued directly to it using a poly construction adhesive. The edges can be sealed with metallic tapes.

Furring strips can also be added, allowing insulation to be installed between them, and subsequently finished with an interior wall surface of your choosing. The furring strips can also allow you spacing to run wiring chases, if you choose to electrify the DR.

You have an advantage with your present interior wall surfacing. The outer wall skin is protected from interior denting, and is more finished than the open studded construction commonly seen in DRs. Many trailer owners would like to have a finished wall surface like yours.

Most air conditioning supply houses sell a product called ductboard. It has foil on one side and is 4ft X 10ft. It comes in 1" thick with a "R" value of approx 4.3 and 1 1/2" with a "R" value approx 6.3. When installed using the foil tape at the joining seems it makes a great vapor barrier and stops air infiltration. It cuts easily and although it is rigid can be shaped to fit many different angles. The1" should sell for approx $35-$40 and the 1 1/2" for $45-$50 per sheet.

The point is that with a small space such as a LQ, we are not as worried about getting the most efficient insulation possible.  The cost trade off just don't justify it.  It is very easy to turn on the furnace or A/C and over power the enviroment.  Who cares if it cost us $2 more in propane for the weekend?

Unlike our homes that we occupy 24x7 and that have much larger conditioned spaces and result in larger heating cooling bills. We worry about saving $50 every month of the year on our home energy cost. We don't usually worry about saving $2 for the occassional weekend.

Space is usually much more of the driving factor that saving $2 in propane. Would I convert a 6'10" interior into a 6'8" trailer to save $2 in propane.  Probably not. The space has more value to me than what I will save in energy.

Insulate the trailer as effectively as you can that doesn't destroy the functionality of the living space. If that means putting up a 1/2" foam panel that meets edge to edge and just taping the edges, that may be more efficient than putting up studs and inserting 1.5" foam between the framing members.

We have the ability to heat any trailer ( with or with out insulation) So having insulation is often more to stop condenstation from forming on the inside walls than staying warm. So pretty much any thermal break that will stop condensation from forming is usually enough for a LQ.

We have the ability to heat any trailer ( with or with out insulation) So having insulation is often more to stop condenstation from forming on the inside walls than staying warm. So pretty much any thermal break that will stop condensation from forming is usually enough for a LQ.

This is probably the most important consideration. Ask anyone who has slept in an uninsulated goose area, and awakened to find the whole lot covered in a light coating of moisture. The warm moist breathed air hitting the cool metal skin, condenses and wets everything inside. This will be aggravated if the area is artifically heated, allowing even more moisture to be stripped from the interior air.

The interior air must not be allowed to touch the exterior metal skin or any interior metallic structures attached to it.

One $30 ceramic heater can easily warm the interior of a 13" LQ. As PH said, the small area is easily heated.

So what about just using the spray foam insulation you can get in a can?  I have seen a couple people use that...

Spray foam from a can is difficult to control and fairly expensive.  If does offer a good R value for the thickness, if you get a consistent even appication. But it is mostly designed to fill holes and penetrations. Not coat an entire wall.  Think of the cost of $8 for  single can that might fill one stud cavity. Vs a 4x8 sheet of 3/4" foam board for $12-$15 that will fill 3 stud cavities. You usually are better off cutting foam board into the space and using the can to fill the small holes.

Insulation companies can spray urethane foam in wide brush strokes.  It goes on like water and immediately foams up. Depending on how much they spray on, it will swell to the various thickness.  This is OK behind a sheet rock wall where nobody will ever see it.  ( or in your case behind some sort of paneling) But getting an exact thickness is hrd to control.

The problem with most foams is that it is very difficult to remove any excess  So you have to be very careful about it's placement. I love a thin layer of it in any new home. Since it basically GLUES all the wood members together. But we usually only put in 1" of foam then put normal fiber glass bats in front of it to finish filling out the wall cavity.

Two types are made. One is expanding and it would be tricky to spray the correct amount so it doesn't expand to much. This would help if exterior noise is a concern.