The base is a drain flange. This thing has holes in all kinds of different places, so this could fit any number of boats. However, on my Pyranha, the screws fit perfectly snug against the center column. It took 2 more connectors to get the threaded connection. The poll has a holes drilled all the way around the bottom. The holes create a weak point at the bottom, so it will hopefully break off there if I hit a rock, instead of breaking my boat. There's a rope running through the center that comes out at the top and bottom to work as a camera leash. I still wanted to have a handle on the back, so I just screwed the handle into the side of the flange. I stuck foam to the bottom of the flange to make a better fit.
I made two 4 inch washers out of some rather thick plastic for the inside of the boat. The plastic washers aren't required, but they give the screws a larger surface area and help prevent cracking the boat.
I haven't had a chance to try it with a camera on the water yet, but the mount stays pretty stable. There's almost no wobble. Ever since I put the base on, I haven't taken it off. It's so low profile, that I don't even notice it. After making it, I could have cut down the female threaded section to make it even lower profile. It sticks up a little and really only screws in about an inch anyway. I thought about making it a smooth dome with Bondo, but I really wasn't interested in that much work. The edges really don't make any difference, and keeping the extra holes available means I can maybe put this on someone else's boat.
Make sure you GLUE your pieces together. I didn't do that with the prototype and lost it. PVC doesn't float. Good thing I tried it without the camera first. The final mount also has foam in the tube incase the lease fails; anything to save the camera.