If you go to the rv store, they sell a nylon wedge that is held onto the bottom of the door with a screw. It will lift the door as it hits the threshold and probably solve your problem.
Ron & Charlotte
WD8CBT since 1976
32' Gulfstream Ameri-Camp & 05 Ram QC LB
I started with nothing and I still have most of it left
I never fail, I just succeed in finding out what doesn't work