<< the full Westy models with a battery under the front passenger seat
have a different setup than you describe. They have a riveted in frame
around only the battery area. A cover plate is screwed down to this
frame with a rubber gasket sealing the entire perimeter. This all works
to seal the battery away from the passenger compartment. Then 2 vent
holes are made that connect the battery area to outside air in the
wheelwell. That setup is what we are called the "sealed and vented
compartment". The regular battery compartments have a hinged access door
that is in no way sealed, as you say.>>

Mark ,

My Westy in no way shape or form has a separate riveted in frame with a
sealed compartment area.
It does have a thin rubber gasket under the lid,and the lid is riveted
to the end of the battery box.
I think it does have a vent hose, but for sure I wouldn't consider it a
"sealed box"
as I would consider a marine sealed battery box to be.

Other than that vent hose I don't see any difference to other Vanagon
battery compartment area's.