I have a 2002 classic 30'. Sometimes the screws in the door hinges will come loose. I have also had to adjust the striker plate that is the place where the door latch mates to the door frame. The striker plate will loosen and move a little. I also have a problem if I do not have my stabilizer jacks down correctly, too much pressure on oen end or the other.
I would suspect the striker plate before attacking the door.
Rebee - WBCCI #1325
2002 Classic Ltd 30'
2007 Dodge 2500, 6.7 Cummins