I resealed the coleman a/c on my rv last year however the leak has started again. I think the problem is that the 30year old roof has sagged under the a/c weight . I am considering making a plywood te...
Rod, If you still have that Holiday Rambler (and I wish we still had ours!) that roof should have metal trusses and hopefully metal framing around the A/C "hole." Think I'd consider using synthetic material, though. StarBoard is a brand that comes to mind. It's gotta be done well, though. You don't want to trap water between the roof and your new patch.
How big were you planning to make this? It'll take a fair bit of margin to keep the patch from distorting.