It's a good bet that the damage is from the roof down through to the floor. It's not just fixing the roof, here. Walls, ceiling, framing, and part/all of the floor will probably have to be removed and replaced. It's not trivial and it won't be getting any better without fixing the whole slide out.
The work itself isn't difficult. It's just the amount of pieces and time involved. If the OP does start on this, make sure that you maintain plumb and squareness when assembling. There was an owner of a fiver on this Forum that replaced part of his roof and front cap. When done, the siding was so out of square, the joints were inches apart.
Replacing the rubber membrane roof is fairly easy, certainly in the realm of a DIY'er. Make sure the underlayment is flat with no screw heads above the surface or large gaps between sheeting joints. Apply adhesive to one half at a time, let set as to adhesive directions, flip membrane half onto adhesive and roll it down. Same for the other half of membrane, rolling from the middle out to remove any bubbles. The membrane edges are typically held with aluminum trim strips screwed down through the membrane into the framing.