mounting a glass hood scoop on a steel hood

The cracking problem probably has to do with the different rates of expansion and contraction under heat and cold cycling of steel sheetmetal vs the fiberglass scoop. What can possibly bridge that gap between those rates is using JB weld to bond and rivet the scoop in place. This should help bridge that rate of expansion, then use an autobody filler such as dyna glass over the JB weld glue joint.