Suggestions for sagging roof

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

As other have said - real fix is too expensive. If your not going to travel then you might away with using a water proof tarp combined with something to support the tarp and keep rainwater from pooling on the tarp. Ain't fancy/expensive but it should suffice for a while. Lots of parked trailers that have the entire top shrouded in tarp.

I have replaced a roof on my 73 TT in 1986 due to the same issues you have. Its a job, not difficult to a handyman with basic carperntry tools.
MY job was a 1973 20' TT with a n aluminum roof made up of 4' panels fold seamed togrther that leaked over 2x2 lumber tapered to 3/4" at the walls.
I removed all the roof to the inside cieling panels and started over. I framed the roof with 2x4 lumber with 1 1/2 arch at the eave to 3 1/2" at the apex which allowed greater insulation and rain snow shed.
Being that campers are built from the inside out, the new luan ply ceiling panels must be placed first, then the trusses, framing, wiring insulation , lastly roof which I did with a 1 piece aluminum sheet roof.
Bought that unit in '78 for $5k, full timed in it for 2 years sold it in '89 for $ 4500 better than new.
Asagging roof is due to thin joists
For me a rebuild paid off very well.

Wow, thank you all for the great ideas, feedback & support! You've given me so many things to think about. I really appreciate the help!