I wouldn't use fiberglass. Alum. flexes to much and a fiberglass patch will seperate over time. I would plug the hole tightly and apply 3M 5200. I did this to a little 12 footer I have and it hasn't leaked in 10+ years.
How big a hole is it? If it is small enough, put a bolt or rivet sealed with 3M 5200 in it. If it is too big, make a cover out of aluminum sheet, and pop rivet it on, sealing it with 3M 5200.
Fiberglass patches are to stiff for a flexible aluminum hull.They will leak or crack over time.Bassboy1's response is about the best if it's a big hole.