It's really hard to tell how extensive water damage is by looking at surface damage. You really have to grab a flashlight and pull some panels to determine the extent of damage. It's possible that a leak was caught and fixed before extensive damage was done, but it's also possible that a lot of hidden damage occurred before repairs were made. I've always kind of felt that if the owner didn't care enough about their RV to repair the obvious surface damage, they weren't likely to put much effort into trying to find and fix any hidden damage, but that's certainly not a rule.
I just had two spider cracks on our windshield repaired about two weeks ago - both the result of a semi-truck getting onto the freeway in front of us. Each of them was about 1/4 the diameter of the crack shown in your picture (if that). After paying $45.00 each for the repairs, I did some research into buying my own windshield repair kit, because I think you could repair a lot of the smaller cracks yourself.
Everything I read from people who seemed to be "experts" indicated to me that a crack as large as the one in your picture would be too big to repair, because the epoxy won't be able to travel the length of all those cracks once injected into the center of the crack (But I'm no expert). I guess there's also a time-frame that cracks should be repaired within. It has something to do with the epoxy not adhering well to dirt and other things that have worked their way into the glass over time.
Kev