I did make and still have a GPR garage/beach dolly.
I made two sets of foot pads for it which simply slide in and pin in place. One has flat pads as this stand in pic the other have heavy duty castors.
Right now its sittin in my living room with 3 of my R/C boats setting on it.
The castors that are in the pic ARE NOT on the stand. I up graded them to metal hub castors with rubber wheels. The blue ones are all I had at the time of build. I did carpet the wood bunks.
Here are some early pics.
30 bucks in castors.. whats it worth???