I'm surprised it doesn't come with one already. Usually, they put those in a pretty beefy spot. If it's not properly reinforced, it may flex and crack the gel-coat. Depending on how thick of fiberglass you're mounting to, I'd add some additional aluminum on the inside to spread the load out. I'd also sealant around the hole upon installation. I'd say if it's 1/2" or thicker, you'll be fine. Less than 1/4" and I wouldn't mount at all.