It's just a 1" ply base painted black with 4 2x4 posts 9.25 long. Tire slides over that so it's not actually sitting on the carpet. Then a 1" ply pedestal cut just smaller then the base of the seat-use bolts and the seat frame to attach through the ply pedestal and attach the posts to it. When tightened down its just about 1/8" lower than the width of the tire so it holds the tire in place and the seat isn't touching tire and tire isn't touching carpet. The base also extends a bit back so you don't lean and tip it over.
Real simple though assembly has to be done in a certain order. I could clean it up a bit and upholster the wood too but painted black it's low profile enough for my manroom that I'm fine.
You could easily adjust to fit any tire though I'm not sure I'd wanna go much higher than these.
Seats were 236 with free shipping on eBay, wood was like 25 and 10 in hardware. More time spent figuring it out and going back and forth from lowes than really cutting and assembling.
'10 Chrome Orange Evora
3020 lbs wet, 285 whp, grins for miles