We have had front window water leaks in our GS Yellowstone Ultra Class C. We have no front window because factory installed an entertainment center above the cab. But we have two windows in bunk area on either side of cab, and we have had to repair them.
We had a bubble in the fiberglass exterior but no damage to the inside paneling. Removed the window and dumped Gorilla Glue under fiberglass bubble and clamped for a week with lots of clamps. It worked. Reseated window using white 70% elastomeric caulk and it has held water tight for 3 years. Repeat on other side. Replaced the deck on the bunk area with new stronger piece of plywood because water leaks had caused a sag under the weight of the entertainment center. No mattress so no mildew problem.
Cost was just lots of caulk, glue, and clamps, plus 2 sheets of nice 3/4 inch plywood. There is a special glue sold online for 100 bucks especially to solve the fiberglass delamination problem but did not purchase.
Originally Posted by lindana
Overcab window has developed a leak. Outside wall under skin both sides of window is flexible (moves when pressure is applied) but inside wall is solid. Very little dampness on bed floor. I am being told I will need to replace whole front ($4500), but curious as to why inside is solid? Wouldnít dry rot affect the inside wall?