Why not add a heating room in the likeness of an addition ?
I mean cut a hole in the trailer and build a room outside that can hold practically infinite weight, perhaps it's even a brick room that is fire resistant.
The hole in the trailer can be a door that is closed in the hot months and removed (or opened) in the cold months. Box fans can be placed in the door hole to drag the heat in
Mod the trailer
And when you go to resell it (if you resell it) no one will think an "extra door" is so wacky.
What do you think of that ?
Cheers,
Craig