It's generally not allowed to drive around the Fort with a vehicle, although it is allowed with the Golf Carts. That said, however, is it done? Sure, but again, it's discouraged because you really need to go slowly, particularly in the loops. Also there is really no place to park (or even pull over) in a vehicle other than the "Sites" so maneuvering around is a challenge particularly if you wanted to spend more time in an area looking. Also consider others pulling their rigs in or out can cause additional problems.
I don't know as if your MB will allow you direct access to the Fort through the main gate, so you would have to go through security. If you have a reservation, you can park in the main lot and catch the bus. I suppose depending upon the CM at the security gate, they may or may not allow you access if you give them a reason of "You want to drive around and look". You best bet is to express a desire to talk to the CMs in the building about a future visit, and then get their suggestions about how to check out the rest of the resort area.