Re: Do I have to predrill before running screws into fiberglass
As for the size of the hole in the fiberglass, making a hole larger than usual for wood has already been suggested. There seems to be no table for pilot holes in fiberglass.
An method that has worked for me was to acquire a scrap piece of fiberglass, start with the appropriate pilot hole for hardwood and drill and test increasing larger holes until the more or less optimum hole is discovered. That hole size seemed larger than I had anticipated.