[jsb5717]

I think the windows are a great place to start to investigate water penetration. Seals around roof joints are also good. If there's water where it shouldn't be then a seal somewhere isn't performing.

RV's are built with a single line of defense against water. Anything that penetrates the roofing material or wall (like a vent or a door or window) creates a necessary weakness in the exterior barrier. The single application of caulk or tape to keep the water out is all there is. If it isn't properly applied at the factory, or if it fails, there is no redundancy to manage water back out at there typically is in S&B construction.

A good cap-bead around the slider side windows will help but is a temporary fix. A removal and good re-seal of the window frame is your best bet. If you pull the window you will likely see where the water penetrated if that's the culprit.