Perry Tart : Your problem IS the solution ! 1st get a trailer that is big/strong enough to meet your needs, and well within the towing capacities of your Dedicated Tow Vehicle .
Second work on a reproducible process to quickly level your trailer after you arrive on location. A well braced trailer will outlast one where that step is skipped .
My next suggestion is to go with a series of metal or wood Trailer bows //// See link below
https://iceboats.files.wordpress.com/2014/11/trailer-for-yellow-bird_img_6.jpg
This can then be covered with Canvas, Tarps, or the Advertising banners from Roadside Billboards ! ( Your on your own for door construction ! )
Assuming a certain amount oF D.I.Y. skills in your group, the bows can be made by carefully splitting and planning down Many types of Saplings , especially Cottonwood and
Willow, with extra points for finding and using Coppiced saplings - Much of the skills are interrelated with the skills for Wattle and constructing "Hurdles''
I hope this is Timely and useful, For the good of the craft ! Big AL