Having some experience doing this type of repair, like others have said, only you can decide how much to spend. My rule is.... does the repair cost more than 40% of the purchase price, and if so, will the repair add value to the rig at all?. If these questions end in negative values, then I would dump it. This is not condensation. You have a roof, water pipe, vent or window leak somewhere, and it's been that way for awhile to do that much damage.
Best of luck as you move on to your decision.
2016 Outdoors RV Glacier Peak 26RLS