It seems the only real OFF-ROAD RV trailers come from Australia. They certainly have some very rugged units...
LINK
These units however are very expensive and of course being from Australia are wired for 220VAC appliances...
One in particular has really got my attention and I may start seeing what I can do with my Starcraft RT14 OFF-ROAD Trailer by adding some of these features to my trailer... My POPUP main unit is a 12-foot box with a front deck. Adding some of these features shown here would sure make up a great WAR WAGON for me getting back into the places you have described. My RT14 trailer has all the comforts of home the big trailers have just missing abit of elbow room.
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Roy Ken