If that's the case, then the issue is more complicated in terms of stablizing the cradle and the mast.

Larry's suggestion about the jack stands provides the advantage of easy verical adjustment. You'll still have to i) spread the loads at the base of the jack stands; ii) stablize the jack stands; and iii) then tie-off the mast with diagagonal lines to the beam of the boat.

I've seen pictures of PVC type assemblies that are "fitted". In the aft section usually in the cockpit well; and forward you have to find someplace near the bow (that's more complicated with your nice toe rails).

I'd worry about the splice being supported, especially while "bouncing around" or if you cant assure that the mast sits in the cradle so the long cross-section is vertical and creates a beam.

This problem is addressed most often with boats going through lock and canal systems. If you search you can see some assemblies of varying levels of sophistication.

I like the PVC's appearance; however, if you're moving the boat over the road (or in a seaway), it is more bittle than wood would be. PVC could be somewhat lighter if you use bigger sections of Schedule 40 pipe (don't use the thinner walled versions).

Again, the issue is as much dynamic loads and keeping things stable. The mast was designed to be vertical (and in column).