[77newell]

I had somewhat similar problems on the 77 coach I owned. The really nice thing about this era or vintage is that they come apart down to the steel structure very easily. You can cut out and replace the structural steel under the water bay if it is rusted too thin. More likely you just need to clean the rust up a bit and then use a rust converting primer. The big thing in my mind is to then build up the floor in a way that controls how any water leakage flows so that it drains out at a specific point clear of the insulation. I put blocks of blue foam under the floor between the structural steel. That is not as good for insulation purposes as covering the structural steel too but I never had a freeze problem even in zero degree weather. BTW, for the floor I used plywood with several coats of WEST epoxy on all sides to basically create a waterproof tray so that leakage was contained and could not sneak around the edges and go who knows where.

One other thing I did was paint the structure with used engine oil as a rust proofing, the oil soaks into any rust still present, is cheap, and stopped rust in its tracks. In the summer if you put a coat on, then drive down a dusty road, and then put on a second coat of oil it's double protection.

If you have questions please feel free to ask, there is lots of knowledge and good will here.