I had to carry my spar up and down the Lake Champlain Barge Canal and some of the Hudson 2 or 3 times. Not only could you get some massive wakes on that trip, it's amazing how much quicker a sailboat with the mast down snaps from beam end to beam end in the trough of a deep wake. A big stick loose could do a lot of damage to you and the boat.

So what I would want is a way over triangulated frame and lashings that would secure the spar against huge side to side forces. If you can figure that out with PVC, that would be fine too.