I installed cannons on my 1999 180 horizon. I bolted a small piece of 3/4 inch angle alum. to the inside of the gunwale, that made it as wide as the mount. Then mounted the cannon mount on top. 2 bolts through the fiberglass and one through the top of the angle. I will try to go down my boat (in storage) this weekend and take a picture. I've had them for over 10 years and never had a problem.
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1999 180 Horizon LS 4.3 L GL Volvo SX
1994 Powerstroke
2002 Jeep Wrangler
not@work.gonHappiness is an Empty Boat Trailer!!!