2" pvc would hold it but flexing a lot. 3" minimum. 4" perfect. But if you put a joint in the center anywhere that joint may give out. PVC is made for internal pressure. All the glue has to do is mostly keep the pipe from slipping out of the joint and of course leaking. Short answer.. the 2x4, 2x6 on edge and carpet are best. I've dozen canoes on 2x4 edgewise but all are under 90lbs.