I recently acquired an older double wide with aluminum siding. The siding needed painting, and I was amazed at how easy the smooth aluminum siding was to paint. I have a sprayer, but chose to brush it because it was so quick & easy. I doubt the entire place took much more than 2 gallons of paint. Vinyl is probably just as easy to paint.
It also needed a roof. I got some quotes on a metal roof. The quotes seemed too high, so I decided to install it myself. Installing a metal roof is very quick & easy since the metal panels are very lightweight, and being full length they cover a lot of square feet. The chore was removing the old shingles & hauling to the dump, two layers...
Metal is probably too expensive for your project, but was a good choice for my DIY job. I've also been installing laminate flooring, which really looks great in the great room. It was only $1 per sq. ft.
This place was a gift from my dad for us to have as a vacation lake home. I never thought much of trailers before, but now I realize that they can be fixed up to be pretty nice, especially if in a nice setting.