Depending on the size of your dressing room, if you are looking at pre-made cabinets, you may want to look at bathroom cabinets.  They are typically not as deep as kitchen cabinets.  I believe kitchen cabinets are around 22" and bathrooms run at 18".  Another thing to consider is the material that the cabinet is made from.  Pre-made cabinets are usually constructed of particle board.  This is heavier than wood and due to the vibration and movement of the horse trailer, the particle board may not hold up as well where it is joined as wood will.

A while back, someone on the board said they made model cabinets out of cardboard.  This sounded like a good idea to me, as you can truly see how much room you will need to move around in the LQ before the real cabinets are installed.  Barring that, make a scale drawing of the floor space and lay things out.

You can check Home Depot or Lowes websites to get an idea of cabinet size and construction.  There are lots of threads on this site where folks have detailed their LQ construction projects.

Our LQ cabinets are the same as WD's, with depths of 12" top and 22" bottom, outside dimensions.

A few years ago, I helped a friend install a LQ in his trailer. We purchased non assembled knocked down cabinets. They were foreign made and had solid hardwood face frames and raised panel doors, with the cabinets and shelves made of veneered plywood. There was no chipboard at all.

Originally they were assembled using locking cam hardware. Because they were disassembled, it was very easy to modify the sides for any depth that we needed before the assembly. We finished them off with glued and screwed joints, and they look and continue to work very well. The pricing was comparable to the pre made particle board products commonly being sold.

Gard

Trying to keep as much floor space as possible, I made the uppers cabinets 12" and the base 18".  The 18" width was enought to get the bar sink installed with some counter around it.  I built my cabinets out of solid oak and plywood.  PM your email and I will send my Power Point Presentation.

Turfa

My "LQ" is a 4' shortwall and has to hold cooking stuff, tack, picketline, folding chairs, sleeping and clothing.

I came across some WONDERFUL resin (plastic) cabinets made by SunCast. Sears carries them for the garage organizer, but SunCast makes a wide variety of cabinets. The base cabinets are quite deep - deep enough to store a hassock-type portapotty; 5 gallon flatbacked pail; my Coleman hot water on demand, and many other items. The doors overlap and the RH one has a catch to hold it closed. The cabinets come with adjustable shelves and with knock-outs inside on the back panel so that you canscrew them to a wall. The base cabinet top, is contoured so that they cabs can be stacked securely. They make cabinets that are less deep as well.  I have a set of drawers on one wall and 2 waist high cabs on the opposite wall. I also have a patio storage bench.

Love the stuff. MUCH better than sterlite or the other brands.

I have purchased these items through Sears, and from KMart and Walmart. Suncast.

Mine is a goose neck four horse slant with a 10 ft long wall and 6 ft short wall in it, I just ordered some cabinets from Lowe's yesterday and they are going to be 22" deep on the base and 12" on the top

Jim