So I've been using Autocad since Release 10 and have a personal copy of Autocad 2010 on my laptop I use for drawing houses for people as my home based business. My software came with the Revit Architecture Suite to include Revit Architecture, Autocad, and Autocad Architecture.
While Autocad is my primary Go-To program, I'm thinking using Revit Architecture for something like tear drop trailer would have it's place as well. The difference is mainly what I used to have as a tagline "Give a man Autocad, he'll draw you a floorplan, give a man Revit, he'll build you a house.
Revit Architecure uses things like wall types that you can freely design so you might have like a 2x2 for the main construction and whatever you have on the outside for the finishes wall, as well as any insulation you might want to put in the wall and whatever finish you want to put inside the trailer itself. That way, if want to draw a wall, you draw it in a plan view say 8' long and you select the wall style (family) you want to use and Revit puts in the interior, insulation, and exterior at the height you designate for it to be. Ohh, and it's all in 3D so you can spin everything around and get different ideas of how things are put together.
The biggest trick is to find wall types, flooring types, ceiling types, windows, doors OR create your own with a little bit of work.
If anyone is using Autocad and they're having any problems figuring out how to do anything from writing your own custom commands to pretty much anything else, drop me an email or leave me a note and I'll get back to you the next time I log on.
All these other programs are trying their best to imitate what AutoDesk has done with Autocad for over 30 years. Some come close, others, not so close.
Student versions are available along with free 30 day trials so if you have a one off design you want to get drawn up, you should (With a little help) be able to handle it.