3 Layers on the inside for a narrow slice is more than sufficient. On the outside, You may want to sand/grind a bit and then a apply a layer or two of 1.5 oz CSM then sand and fair and then Gelcoat to ensure you have adequate bonding and a bit of additional strength. Won't hurt anything. No 1708 needed on the outside IMHO!! How thick is the glass on the hull?
