Repair all depends on your skills and available time. Anything can be worth doing... or not.
Only you can answer that. Some water-damage projects will be very involved and take a lot of work, some might be easier.
To kep water from pooling just crank your tongue jack up so the camper is slanted and the water will just run off. You might still get pooling where the AC dams up water, but should not be as much.
I had a very damaged roof on a trailer. I had to pull entire portion of ceiling out. Rusted steel frame had to be reinforced, new ceiling panels put in...
Under the AC unit I put a 3/4 inch board all the way across the ceiling, and this was un-necessarily supported by a board down the wall. This board is able to hold up a lot of weight and I could safely walk on the roof there with no risk, and the roof was very solid there. I ended up painting it to match, but these pics are better for illustration.
I have a cargo camper that I put a roof AC on and was able to just weld in new 1 inch square tubing to have more supports under the AC unit. However, this was on an undamaged trailer with no rust and no water damage. It also is very stable and can support more than just the AC unit.
Here is pics of trailer damage, I think pics speak for themselves. This is just to give you ideas...
See the brown board behind the AC unit on ceiling.
See brown board running across and sits on top of the brown board running up the wall.
I used this camper for a year with no issues, then sold it.