Most any quality epoxy should do the job. I just bought a tube of the stuff that 3M makes to attach body panels on fiberglass cars - #8115 Panel Bonding Adhesive. Marine stores also usually have an epoxy adhesive - they are quite common on fiberglass boats. I like the Marine-tex
brand myself. I'm talking about a paste-like, two part adhesive, not liquid resin.
Plain old automotive Bondo
(body panel repair) should also work nicely. It, or a similar body putty, should be available in most any auto parts store.