I made one of these window mounts using a ball head and a Scotty Portable Clamp on Bracket No.249. For your boat. Costs around $40 canadian It comes with stainless steel 1/4 bolts. Which fit the 3/8" to 1/4" reducer bushing if there is one on your ballhead..No holes to drill... Then use felt used on the bottom of furniture to protect the class or whatever you put it on... opens up to about 2 inches... for the money its great, works well. Just my opinion but it works well...