Box, do you have a mechanical linkage or air control?
Are you locked out now, or from time to time?
If you have the mechanical linkage, you may have the same problem I had on
my first BB, which was a 1981. If you pull the door shut a bit too vigorously,
the linkage will go over center and lock - just like you lock it when you start driving.
On mine, there was a little hinged flap -- a plain hardware store hinge, really --
that could be folded down to keep the lever from moving to the over-center position.
I learned to secure that hinge in the down position with tape to keep friends from
locking us out. If this is your problem, you may need to rig up such a "stop",
and use it religiously. Better yet, put a spring on it, so it always goes to NO-LOCKOUT
when you open the door after driving.