This is a rendering of a doodad to help with righting the mast. It's specific to the P-Cat, and would have to have a different geometry if used on another boat.
The idea is to create a pivot point along the axis of the mast hinge, and place eyebolts at either end of that axis. The eyebolts are strapped down to the trailer and forward to the forestays. The T-shaped framework rests on the deck of the boat. (I'm planning to split some Tygon tubing or fuel line tubing and slip it over the bottom of the flat part of the T to act as a rubber foot.)
In use, one pair of trapeze hardware is unclipped from its shock cord and is tied onto the eyebolt instead. Once drawn tight, this constrains the mast to move in a fore-aft plane as it is raised or lowered.
The width of the beam is such that the 10 degree mast-to-stay angle of the P-Cat is maintained down past the eyebolts and on down to the straps that connect the structure to the trailer. That way there is no torque on the side plates.
The side plates will be made of 1/4" 6061 aluminum. The cross-tube takes very little force, all in compression, so it will be made from pretty light stuff.