Landlord, it would work great for what you are asking about. It needs to be left in the "Clamped in Place" mode overnight and you will be gooda to go.
Maybe a shorter time in direct sunlight.
Rocky, I don't know if it would work on fiberglass. I know in the OLD DAYS, fiberglass and metal heated and contracted differently and that is mostly why all the fiberglassed on hoodscoops cracked off after a year or so. If you are thinking glueing in tinwork to the fiberglass, it just might work for that. I know I have mentioned it before, Evercoat makes a "Fiberglass Resin Jelly." It is resin that is thick like body filler so it stays right where you apply it. It is the best thing to ever come along for fiberglass work. You can apply it over top the mat so it just lays smooth like glass so you don't have to finish it off if it is on the underside of the body. It could be used as a glue without mat for something like that I bet.
One more note, most of the panel glues are not to be used out in the painted area. In other words, if you splice in a qt, like at the sail panel by the roof. You will have to weld that area, and finish with body filler as the glue will show a line in the sun even if you have body filler over it it will cause a ghost line there.