I can tell you a better option than a bolt if you have a ram mount already.. its called the ram mount claw. There is also a sleeve mount meant to go over a round rail. Both would be a better option than a u- bolt since they don't apply any direct pressure to the inner pivot pipe. However I went to lowes before I knew about those items and purchased u-bolts that were a little wider than the od of the pvc pipe and long enough that it allowed me to bolt to the base mount. I had to grind notches in the base mount slightly since the bolts were not wide enough to go around it. Below is what I came up with. The screen shot is the rail mount I'm referring to.
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