What about a vehicle that you constructed, not out of bricks themselves, but in some form of an editor. As in, a GUI that pops up and lets you customize a vehicle to be any shape and size you want based on bricks. As in, say I want to make a literal "boxcar" the GUI would pop up, say, "/vehiclegui" or something, and you can edit the physical aspects of a vehicle to make it into an actual "box" with a mountpont in the middle.