I have some experience with Solid Works and Pro-E (hate it) and am in the process of using/learing Solid Edge (for work)... I might be able to help on some stuff. Sounds like a fun project!
Drop Box is a good medium for sharing stuff and it's free. I would imagine we could set up an account we can share access to and there ought to be enough space to put any/all models in... animations on the other hand, those can get humongous in a hurry.
If going with an open source method, the models saved to the shared directory should have some sort of universal format, such as IGES or STEP. We could create a sub-directory for each section/component of the truck and they could all feed into an assembly - although, I can imagine the assembly will quickly get hosed if multiple people are accessing/changing the part files w/o addressing the assembly linkages...
ANYwho, I like the idea. It'd be fun to see what kind of mods people could come up with in a virtual world. Which also reminds me, I wish I had a 3D printer...