Cheap Fix for Big roof Problem

Thanks for the advice AND the pic! We are worried about using the wrong sort of adhesive for each thing--such as the rubber skin and then glueing/tacking the gray plastic curved stuff back onto the plywood. my husband was thinking liquid nails but would it be compatible with both materials AND whatever we put over for the top. Talked to the RV guy at Eternabond today and he suggested WebSeal as it is meant to be coated over within 48 hrs. He also suggested using rubbing or denatured alcohol as a cleaner! The primer however you need.