Attempting to modify bedroom of old Dutchmen

I had a 94 31' Dutchmen Classic for 18 yrs. What your wanting can be done, of course the labor will be the biggest expense. Building a wall is not a big deal. Since you already have damage, I would want to support the ceiling to prevent any additional damage. Give it careful consideration as the damage will probably be far worse than you suspect.

Building a stronger wall you could consider a Murphy Bed that folds up against the wall. Then the room could also be a play area during bad weather and maybe calm his fears.