You're talking about a regular handheld, right? I'll try and track it down but for about 25-20 bucks that have these 3 inch suction cups for salt water fishing that you pump up to tighten the grip on a smooth flat surface. I've seen them use 4 of them on boats before with a rack to hold up air tanks for scuba diving They are sturdy. They also have a 1/4 inch screw hole in the middle of them so you can mount your handheld on there. Best thing is NO DRILLING but IF you want to drill, make sure you put some kinda backing on the inside of where you mount it. I was talking about using a piece of sheet metal for support but a few on here said to use some plywood. Main thing is support the back side of it so it won't pull through and damage your boat