Auto body repair & detailing: installation of fiberglass scoop, vw baja bug, nuts bolts

Question
Dear Sir,
  I have been trying to find information on installation of fiberglass components on an automobile.  In my search I came across your website and thought someone there might be able/willing to assist.
  The project is a VW Baja Bug.  I have purchased a roof top snorkel, approximately 16" high by 24" long, by 8" wide.  An oil cooler will be mounted in the snorkel and the snorkel attached to the roof, just in front of the rear window.  My question is, what is the best method of attaching the assembly to the roof?
  Once positioned, the assembly will be glassed in and painted.  In operation, I dont want the assembly to crack the fiberglass.  Do I need to mechanically fasten the snorkel to the roof before installing fiberglass or will the fiberglass have the strength to hold it in place?  Not wanting to have to remove the headliner the use of nuts, bolts, and washers is out, but sheetmetal screws (short) are an option.
  I really appreciate any information or directions you can give me.  Recommended instructional material would be appreciated also.

Answer
My recommendation would be to get some thin guage aluminum and fabricate some brackets and pop rivet them to the inside of the scoop ,riveting from the outside, and then to the roof .This will also eliminate the need to drop the headliner.I would suggest cutting the strips 2 in. wide X 6in. long, and bend on a 90 degree angle .This  combined with the glass should be plenty of strength.