To remove the door handle without removing the interior skin panel you can cut a small hole in the inside skin just behind the points that the handle attaches to the trailer. This gives access to the 2 bolts. You will have the wires for the door bell at the lower hole so don't just yank the handle off.
Once your have made the lock change and reinstalled the handle you can cover the holes with standard 2x4 flush electric box covers. Sorry i can not post a picture to help as i have reached the limit for posting pictures.
I you send me a PM I will send a picture of the finished product..
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles