I would definitely choose epoxy (with cotton fiber filler added for strength and thickening) over 5200 for this project
. Even slow epoxy will set faster than 5200, and the 5200 smell will linger for weeks.
I mainly use 'proper' epoxy for boat work, but recently I reattached the foot of a wooden cabinet with some hardware-store 5-min epoxy - also using a bit of cotton fiber filler, and a dowel - and the results were excellent, so for the OP's applicatiion I wouldn't hesitate to use some 5-min epoxy there, which will drastically reduce clamping time.
Another option might be a polyurethane
glue like Gorilla Glue, as long as the fiberglass is roughed up a bit first.
I'm not a big fan of PL adhesives, but maybe I've just had bad luck.