in the Hobie catalog - the fiberglass mast cradle locks down your tiller connector, keeps the traveler car to center and is handy when you are doing a single-handed set up.
Here is the "Cheap way out" using part 3175 as a reference. Take some scrap 3/4 plywood that you might have lying around and build a frame about 8 inch long and 5 inches wide. The frame will rest on the rear cross bar and cradle the mast in between the sides of the box.
Materials are (2) 6 X 8 inch pieces for the sides and (2) 4X5 in pieces for your front and back (or a couple 5 inch long pieces of 2 X 4)
Center up an 8in edge of a side piece perpendicular to the rear cross bar and trace the profile of the cross bar on the bottom edge. Cut the profile so that the piece rests on the crossbar with a little overhang in front and back. The back ideally comes in contact with your tiller connecter when the rudders are full-up. If the back hits the tiller connector and you need to make notches to fit the connector in - so much the better.
Take your 4 X 5 in pieces and glue and screw the 4 inch edge inside your side pieces. The top edge of the front piece should sit about 1/2 an inch down from the top edge of the side pieces. The bottom edge of the back cross pieces should be even with the bottom edge of the side pieces. This will give you about the angle you need and it will nestle the mast between the sides.
Drill some holes, or grab some eyelets, or just bungee the thing down. It should straddle the traveler and keep it from traveling, it will hold the mast down and should keep the rudders from dropping and flopping.
Paint it and put Orange County Choppers decals for a real custom look
I used to sell these for about $15 to cover my free scrap wood materials and drunken labor..... You might even see on somewhere one day...