We have what was a chair from the Big Sky, that belonged to John and Marge. What he did was cut a large circle of plywood, which he attached in a number of places to that round circle of metal with screws. So, now you have a solid bottom. Now, go get some of those slippery discs. place a number of them on the plywood.
Let me tell you, this baby slides RIGHT good. I can move it around in the rig with almost no effort.
Downside, I have to be sure it will not move while we are on the road, it will squiggle around.
Upside outweighs the downside hands down!