Don,
How did you lock the pipe to the floor base to keep it from twisting?
I have similar base units in the back of my boat. I used a lock nut like they use in electrical conduit, but I have to tighten it with channel locks to get it to stay put. Not a big issue, but it would be awkward to do while trolling or moving on the water? Mine has a piece of angle welded to the top as a cross bar so I can't tilt mine up and down but they sit at a good angle to the water.