Being around fiberglass for years. Even worked at a Chevrolet store as a body man.I learned that body fillers are a problem with Fiberglass . They expand and contract at a different rate .Making the panels wavy went in the sun .3M has a vinyl ester filler designed for fiberglass.It goes o smooth and very little pinholes. It is a little harder the light weight fillers.But still sands pretty good .There needed to be a product we can use to straighten out panels when Slick did not have enough film build . The best place I found to get it is Paints Plus 1 800 472 4551 . Auto parts stores do not carry it . Bob the owner is very knowledgeable and keeps up with new products . Has any one else ever used this product . If so let me know your thoughts.