While the dolly pictured is pretty handy and ok it does cause stress on the daggerboard trunk. I'd opt for the Seitech dolly made specifically for Sunfish if you were going to invest some money
. Personally I've used a hand truck with a piece of carpet that works pretty good but your hand truck will get rusty after a few launches in salt water
. I've also got a homemade dolly that works really good. Just use some plastic wheels and some long pieces of aluminum
extrusion and your imagination and you can come up with something.