Ok, Ok, I know this is crazy
, but also kinda cool.......
Here is a wood stove for tenting, which, if someone was really adventuresome, could use in a trailer. You'd need lots of space around it, keep the fire low (twigs?)....
Run the little pipe out a window? More sanely.....set it up outdoors, a nice contained fire for cooking and keeping warm!
All that aside, this is a interesting web site with some trailer friendly ideas. It has a good description of using the Ecotemp L5 portable water heater under the 'backpacking' catagory. There's also a 'living on the road' category, not specifically for RVing but some interesting items with good descriptions.