Vehicle Base
Download:Bungie.net : Bungie Online : Halo 3 File Details
So this uses movable object proximity. When you drive into the base and run into the pallet the dumpster come out of the ground and lifts the mongoose up.
General Stuff:
So all this really is, is a one time use mongoose accessible only base. The reason it is one time use is once you drive in the base and the dumpster comes up it locks the door and mongoose cannot get all the way in the base anymore. I made it so you can not crouch in but still drive the mongoose in.
Pictures:
Overview
Here you can see the tunnel that you drive through and the pallet that you run into to make the dumpster come up.
As you can see when I drove in and hit the pallet the dumpster came up, raised the mongoose up, and closed the door.
Any questions, just ask