I have recently converted my old golf bag buggy into a standup carrier which collaspes in on itself when not in use.
The difficulty using the system is getting enough purchase over the fin to secure the rear of the board into the carrier to prevent movement. A future modification of the rear carrier bracket may solve this problem. The front handle simply rests on the EVA deck with a strap and does not slip around provided the rear is secure.
I have yet to test it with another board and more
gear on top but feel that it should stand up to the test. I have also yet to test it over sand but believe that the golf buggy wheels were designed for that environment and should work reasonably well.
photos are attatched.