hi, I would use "the Mix" the water proofing mix recipe above in the stickies, before doing anything and I am not sure if the window stuff will work to be honest, I painted mine with the "Henry" roof coating for trailers ( without aluminum), Some people use the "black tar gooey, stickie messy stuff. You might want to read up on it. GPW may chime in here, I think the Henry stuff is fine but after I got it at the check out counter It was a little expensive ( for me) but it is worth it. It is like very thick paint. and goes on easy with brush and at times with my hands.
Mary C.