I'm a little surprised this simple and obvious version has not been mentioned. I just cut a hole in my plywood sideboard. The beer sits in the hole and rests on the tube. Just locate the hole where the beer goes about halfway down, before contacting the raft tube. Might not work on all setups, but it works on mine. I have 4 - one on each side, back near me, and the same up front, for my passengers. It's nice to have one on each side, cuz usually one or the other is in the shade.