I can't take the credit for that design. Rick Harper (a local a-cat sailor) chopped up an MC scow dolly to make the predecessor to mine. I'm sure someone else somewhere else has had a similar setup.

The upright on the dolly has a cup that cups the dolphin striker and mast post. In the top/center of the cup are two holes that a "U" shaped pin fits in. Once you get the boat on the dolly, you insert the pin in the cup which captures the dolphin striker and the mast post centered and keeps the boat from tilting back away from the dolly. We've also worked out the angles and spacing (in my case, the lower leg straight down from the dolphin striker support) so that once the boat is on the dolly, you can let go of everything and no part of the boat touches the ground. You can't tell in that picture because of the hull covers but the bows are about 4 inches off the grass.

The t-fitting on the center of the aluminum axle is fitted precisely to the windsurfer mast and they come apart with the removal of a pin for trailering.

Be cautious to work out all your weights and balance points with the boat completely rigged, the mast will change things dramatically.