New vehicle RV take two (WIP please comment but don't pull yet!)

Saw this pull request #2053 and nobody seemed to be working on it anymore.  Didn't get any responses on the comments, so I thought I would try to finish this myself, as I always thought it was strange Cata didn't have an RV.  So far, I think I have the design in veh_typedef.cpp fixed (It had a LOT of bugs, like vp_board on every tile, so it was basically a solid block of metal on wheels) but I'm not quite sure how to add this to Magen.cpp so it will spawn in game.  Can anyone give me some advice on this?

PS - If this is considered stealing someone's idea or otherwise against the rules PLEASE tell me and I'll take it down.  It just seemed a shame to let this sit in dev limbo, and there hadn't been so much as a comment in 2 weeks.