First time buyer - how bad is water damage

I've had 2 RVs with water damage. 1st was an old trailer that the whole floor was rotted out. had to rip out the floor completely, replace the floor beams, insulation floor panels and vinyl floor. Looked pretty good when completed but was a lot of work. Unit still smelled musty until I sold it. 2nd unit was a really nice TT. noticed a bit of a leak, through a tarp on the top intending to look into the problem once it stopped raining. some guy came buy wanting to buy the unit, ended up leaning on the area that had the leak and the whole thing caved in. Dude was a flipper, so he took it anyways, but didn't get as good a price for it. My current C doesn't actually have windows in the cabover just painted. Designer said it looked like a bread truck with out them. Leaks around the front windows is chronic on this style. Enough so that newer models don't have them. If they stopped using glued sawdust and paper to make these things, they could probably work ok, but that whole area flexes too much to really seal it correctly, especially if it's tilted backwards for aerodynamics.