Sportsman Campers

We just bought a camper's 25th anniversary of a friend. He said it had water damage from the hurricane. As we looked at the camper surrounded by trees, we noticed only minor damage. When we got home and started spring cleaning, we noticed several signs that were replaced on the wall and ceiling. Then we got on the roof and nearly fell through. The edges seem real sturdy, but the middle is very soft. My question is what is the best way to check the roof and support beams and how to replace them?

If the roof is in such bad shape, the structural integrity of the camper has all been compromised, and your safest method would be junk. Unfortunately, this is also the cheapest option.

There is not much of a friend, unless he was unaware of the damage.

Most campers have 2x2 wood wall and roof structure. I would pull down the damaged panels inside and check for damage behind them. If you can build things with wood, you can repair the damage for a low cost small.
Perform a search for the restoration of vintage campers, you'll find some good photos of work in progress and be able to decide if you want to try to repair it.