You've probably already solved this issue, but for gluing styrofoam to fiberglass
, Great Stuff Low Expansion Foam in the red can -- the spray foam used around windows
and doors which can be bought from Home Depot/Lowes/etc -- works really well. If you're wanting to glue up large panels, spray and spread it with a disposable spreader, then press your foam panels in place. You'll need to find some way to block them in position while the foam cures.