I could still see my pics when I was not logged in to anything. hmm...
If it is just always sitting then maybe you can get a 2x4 or something and push the roof up from the inside to take the sag out. It all depends on what is inside. If you do this then you will need a board, piece of plywood about 1 square foot, to more evenly distribute the 2x4 pressure over the ceiling or else you just punch a hole in the roof.
Likely you have some water damage, but not necessarily. Things sag over time.
You can pull the AC ceiling piece off from the inside without having to move the AC unit. Then you might be able to look at the roof structure at the 14.5 inch square roof opening. Look for rot or wetness or mold or black mold.
If there is water in the roof, and you ignore it you can get by a few years. The wet, even if you stop the problem at the source, will continue to rot unless you can dry it out somehow. If you dry it completely and stop the leak then you are fine (as you said it stays parked). Rotten wood when dry is just a step away from saw dust, and it has very little structural integrity, but will not do damage in and of itself. Support the roof with an interior something (2x4 or whatever) and you that fix might outlive the camper