Leveling is indeed critically important
before the TM is opened. If level, the shells are much easier to raise and everything (in particular the door hardware) aligns much better. As a person who camps in primitive Forest Service campgrounds most of the time, I seldomly have the luxury of a level campsite so I have to do some major league leveling just about every camping trip. Some tips that have really helped me....
- The instructions for the newer models to level fore/aft first with the tongue jack, then left/right with the rear screw jacks are a great approach.
- Following these instructions is easiest with a stick-on bubble level right on the hitch (for fore/aft leveling) and on the front of the rear bumper on each side (for the left right leveling). The rear bumper mounted levels are great cause I can watch as I turn the screw jacks up/down. IMO, mounting bubble levels on the upper shells is not a great idea because there's too much play in the clamps when the shells are closed.
- Whether you have the new type screw jacks or old-style stabliizers, it's a heckuva lot easier to level the trailer if the rear wheels are level to begin with. Yeah, home made solutions like boards (even stepped boards) do work and don't cost much. But, IMHO, nothing beats the flexibility and ease of transport of the lego style leveling blocks sold by RV stores like CampingWorld. I now have two sets of 10 such blocks and consider them about the most important camping equipment that goes into my truck before departure. Definitely pricey but so handy...I've used them under the jacks in soft soil or where I needed extra height and they're great for building just the right height ramp for the downhill tire.
- Finally, when leveling, I've found it's very helpful if the street side (opposite of the door) is just an eensy-teensy bit higher than the door side. Reason: after a season or more of use, the seal at the bottom of the door tends to develop a gap...if the trailer is level or the door side is slightly higher, water runs under the door and puddles on the floor. But if the door side is just a tiny bit lower, no puddles after a heavy rain. ;D