I used to buy several cars and build custom bodies and interiors. I would use an old iron to heat the plastic enough to bend it to meet different body lines. Or better yet, take a built car and put the whole thing in an old toaster oven puch in the body to make it look like it's been in a wreck. Even got a little creative with rust ans scuff paint jobs. Mmmmmmmmmm melting stuff.
Just got to be sure to do it outside.