How about you can walk around inside it as long as the vehicle is not moving. After the vehicle starts to move you automatically mount in it.
Better
Oh and include a neat little command for the owner of the brick. When the owner types something like /mount while inside the vehicle he will then automatically drive it.
Better, No way
It should have an animation where it puts down two small legs, and from there on, it becomes a static shape, and nothing can move it.
Can space be the command to open the door?
Unfortunately, the collision box of a vehicle cannot be animated.We would either have to make it switch to an alternate model for opened/closed versions.
Vehicles aren't my forte, but this would be interesting as a map. Since I'm on vacation at the moment, I can't make it, but I'll definitely give it a try in TC when I get home in a month.