Sorry to hear this about your camper. I do believe 2006 was the first year of Aluminum frame, as that's what I looked for several years ago, but ICBW. Do your research on it.
I feel for the fact that you got taken on this deal. And it appears you're not the person who will be tearing the camper apart and rebuilding it. However, if the overhead area is solid enough structurally (no bows or wrinkles in the sides that would indicate the frame is actually sagging), just do what you can and go camping. I think venting the bottom of the overhead is a good idea, maybe it will dry out. If you can locate the framing, you could drill some small pilot holes and see if the framing is solid. If so, let it dry as long as you can "sagging" and then you could neatly re-attach the sagging filon skin to the framing with some small screws with fender washers.
This is all a guess, as I haven't seen it, but I can say have had 2 of those campers and both leaked up front, prior to my purchase, to varying degrees and I did some minor repairs, sealed the leaks (upper clearance lights mostly) and used them for years without any issue.
1 of which began leaking on my watch and I ended up drilling small holes to let the water out.
Bottom line, it's not good, but it may not be that bad.
