You can buy latches for Fleetwood cargo doors here.
Cargo door latchesThey should be fastened to the door with 2 metal screws. Put some outward pressure on the latch as you unscrew the screws and they should come undone. There should be no nuts on the inside. You need to take the cover off on the inside center of the door that holds the center opener handle and remove the screws that hold the handle in place and then slip the latch rods off of the handle, then remove the 2 screws on the latch and the latch comes out with the whole rod attached to the latch. Insert the rod into the new latch and feed the rod back into the inside of the door and install the screws back into the new latch and then slip the rod back into the opener handle. Do both sides if needed. No need to try and dismantle any of the door. Good luck I have done 4 latches on my 2004 Fleetwood southwind.