Whenever we are camping, we rarely bother getting the trailer absolutely level, and instead, leave it hooked up to the truck. We usually only camp at show grounds which inherently have somewhat level facilities. If we have to choose on an uneven surface, we favour a slightly head higher attitude for the beds.

If you are trying to always have a level trailer, any of the stick on or screw on levels sold by RV stores will give you an excellent reference. They are inexpensive and easily installed.

BOL  Gard

One trailer we purchased was at the height we like to pull, about 4" high in the front. Our second trailer needed to be adjusted. We hooked up and went to our high school that has a large level parking lot. Our driveway is not level. By loosening the bolts on the hitch and lifting the nose, we were able to lengthen the height of the down tube. We then measured the height from the bottom of the trailer to the pavement. By comparing the front and rear readings of the trailer, we were able to adjust the attitude we wanted. The bolts were retorqued and we were good to go.

Gard

How to level:  I keep a 3' level in the mid-tack and lay it on the running board of the trailer when I unhitch and raise lower the jack until its level.  If the trailer isn't level side-to-side, I keep a variety of 1"x8"x 24" boards in my manger storage area to raise up one side of the trailer to make it level.

Why I level:  Because I have been told the fridge won't work properly if it isn't level, and more practically, my shower drains better if the trailer is level.  If I am in an extremely unlevel spot, I prefer nose-down because my shower drain is towards the front of my trailer.  In the event of an extremely unlevel spot, I keep a sweat scraper in my shower to "pull" the water to the drain.

Since I drag my trailer down Forest Service and BLM back country roads, I'm more concerned about not hitting my truck bed rails on a very uneven road. My trailer is set up a little high in the front to give an couple of inches of extra clearance between the bottom side of the Gooseneck and the top of the truck bed rails.  It was a trail and error approach for me.  The trailer came at a pre set height and I watched it carefull as I hauled over rougher roads and adjusted it higher as I saw the need for clearance. The extra inch or two on the Gooseneck made very little difference in the over all levelness of the trailer or wear on the tires.

A long bed 4x4 truck will need more clearance under the gooseneck than a shortbed. They have more tail behind the ball to articulate  when you  enter into a steeper Nose down position with the truck, while the trailer is still in a Nose high position. If not set up correctly you can catch your bedrails near the tail gate on the under side of the gooseneck.

Having insured that I have adequet clearance over the truck, the only way to get trailer level   ( If I've lifted the front too high) would be to block or lift the trailer axles. I would do this more to insure trailer bumper clearance over rough roads rather than trying to equalize the weight between trailer axles. I think the trailers tow just fine with a slight nose up position.

Now when I park, I have several bubbles stuck on my trailer to indicate if it's level side to side and front to rear.  If not, I keep several blocks of wood to put under tires to help level.