Yeah TPI, you said a mouthful. For sure the roof design, including how it attaches to the walls and the end caps, has been a very weak structure(against rain intrusion) in many RV models. Also, one of my pet peeves is the total design of the method of securing the air conditioners to the roof. There is NO design engineer that I've ever worked with that would consider sealing rain water around a 14 inch square hole by using a foam gasket between two non-rigid surfaces,... using 4 lag bolts which screw into cheap plywood that ROTS. (Of course the bolts are so cheap they easily rust). Rainwater comes in, and pools inside the styrofoam ceiling material, which has sheet brown paper bonded to it, which is glued to the roof trusses,.....etc,etc (I could write an 2 page article on the ramifications).
But, I'm going to bed.....:B
The short version is that it can ruin(total out) the entire RV.