Each of my basement bay doors have a cover plate on the inside that I can remove to get to the handles. It is a molded cover that is larger then the hole and is held on with a couple screws.
If your doors don't have the access you can either drill out all the rivets on the inside of the door and remove the inside cover or you can do some measuring and cut a hole on the inside and then reattach the piece you cut out or you might look at buying a prefabbed hatch cover.
2002 Monaco Windsor 38 PKD Cummins ISC 350 8.3L
2005 Jeep Grand Cherokee w/5.7 Hemi