>>2950758
I have two other ideas which I don't think are as good.
One was to just make a square table and bolt trailer jacks to the side. i think this would look awful and you'd bang into the hand-spinners. plus you'd have to walk around over and over to adjust them all. annoying, but less work to build since you just bolt it to the side of the legs. there's also about 10" of height gain.

my first idea was to put scaffold leveling feet in the legs of the HSS. Then I'd mount casters to the bottom of these.
it would be really annoying to hand tighten each scaffold jack, and i think there would also be pretty bad rigidity because it's just sitting on top of the feet rather than pinned through the side.
however you do get 18 full inches of elevation.

I can't think of a better option than the scissor jack telescoping legs design. I looked at buying real telescoping tubing but it's nauseating how expensive it is. I don't actually need that much adjustment so I figure i'll just drill through the tubing like 5-6 times per leg.