I replaced the original rubber seals around the rooftop door. They were worn OUT. The new ones are the same style with the metal clips, I cut them to go around the corners. The top of my steps have a lot of water damage so I think there was leaking before I did this, but after a big storm I see no issues now. Oddly I see daylight at the rear-inner corner at the edge of the door from the bottom of the steps, but no water gets in.
I also was seeing cracking of the fiberglass roof, super small micro cracking (see close up photo) and so I got Dicor fiberglass roof coating
and the matching cleaner product and cleaned and sealed the roof. Probably similar to the RV Armor guys product. It looks nice and it revealed that I had been leaking around the roof door, I painted the coating all the way up to the vertical portion. Did the same at every joint on the roof. It required two coats, and I had to remove the sink to get around the front AC.
I think the softness of the roof (mine is right next to the roof door in the center) is actually the wood laminate layer having gotten wet. Fortunately the rest of the roof is constructed of steel and styrofoam all glued together. It will probably not get worse like those all wood roofs that need to be torn apart and rebuilt. I did have to take the inside vinyl off the ceiling so I can paint Killz primer on the part of the ceiling that got moldy for water intrusion.
The water also came down the sidewall and soaked into the floor which sadly under the tile is just wood sheeting. Not even plywood. I was able to scoop the wood out with my fingers like putty it had so disintegrated. But I was able to completely remove the bad wood, cut it out and replaced it with new wood. Then sealed the new stuff to the old stuff and re-tile the floor. It's good as new. The steel that the wood is mounted to was painted and hasn't rusted, and the fiberglass exterior didn't care about the moisture either. Probably gonna have to take the refrigerator out as the fiberglass behind it has delaminated so probably got moisture back there too. The wood laminate gets soft when hit by sunlight, but when it cools it's flat as a... a... board.
Not sure there is anything to do, just like the roof, I am not taking it off and replacing the whole top just because there is a little sponginess to a small part.