I learned some great techniques when I was into RC Racing, and I started modding XMods. There are alot of tutorials out there on how to add doors and trunks even hoods and suicide doors.
I\'m sure one of the methods would work for you.
If you can\'t find them, and want to see some of them, I\'ll post a link when I get to it.
Also, there are plastic hinges that work just as well, and can be modelled more easily.