Sagging in cab-over bed area -> how bad is this?

3/4'' plywood is just a band aid.... covering up, further sealing off any chance for the wet wood to dry out. Right now, middle of winter, you have a far better chance at hammering out a good deal on a new unit. Plywood will just bow down anyhow and you'd need two sheets further waisting money because you'd have a seam down the middle.

Oh how I love to argue :)

A dealer with a good repair facility can get that camper back in order, make money after giving you your money spent for a down payment.