That sort of thing is hard to guage from the inside. The roof of your model has wood cross beams, insulation between them, thin sheets of plywood on the inside and a plywood sheath, I believe 1/2", on top with the rubber membrane glued to that.
The reason it is difficult to tell from the inside is that the interior plywood is thin and will "feel soft" when you push up on it if you are between the rafters even if the wood is dry (hard to tell "soft" when the wood is that thin to begin with). The better test would be to go "up top" and see if you have soft spots on the actual roof sheathing. If you can find the leak and get it patched early enough, and the spot is small enough, you may be able to get away with it...depending on where it is. If you have roof rot around where the mass of the A/C is sitting, it will only deteriorate further from the weight of the A/C causing roof flex from bouncing down the road.
As you said, the repair may exceed the value of the TT, but, a good repair facility may be able to cut out the bad spot, spanning the rafters, and replace just that small section for a reasonable amount of $$$.
My biggest concern would be if the bad spot is near the A/C unit...you could well pull into a campsite and find the A/C and a portion of the roof sitting in the middle of the floor with a brand new skylight where the A/C used to be