What is under your TT, cheap islolation?

I have no problems with isolation from footfall with my set up. I have a 5 foot tall Zoethecus rack sitting on a suspended wood floor. But, the rack is actually fixed to a nearby wall using angle brackets attached to a cleat that is, in turn attached to the wall. My table is a Basis Debut.

I generally find that lighter tables with spring suspensions to be the most susceptible to problems with footfall. Big heavy tables that have damped spring suspensions work the best. It is analogous to big heavy cars riding over bumps in the road.

For your temporary set up, I would think that the easiest, and cheapest experiment at isolation would be sorbothane pucks. They do a very good job of dissipating the energy from the movement of the floor without itself oscillating.

I found that the energy causing my problem were horizontal rather than vertical. The equipment stand actually rocked very slightly with the flexing of the floor. If that is your problem, you may be seeking stability rather than isolation. That is where the wall cleat might come in handy. Or the wall mount.

My Linn deck rests on a 3/4" slab of slate of the same footprint. The slate sits on three ball-in-cup feet and the whole stack rests on a 6' side table located along a wall. The three mushy feet allow for damped vertical and lateral movement. The slate, about the same weight as the deck, worked better that just supporting the deck alone on the feet. Sending the kids to a friend's house works even better.

Fishwater,
Like you, I built a sand box with a floating lid to go under the TT. If you are setting the box on a shelf or other flat surface, I suggest you elevate each corner in order to minimize the box from absorbing any shelf resonances. A simple solution is to drive a small brass screw up into each corner of the box from underneath. Leave the entire head showing, and it will act as a small spike.

My sandbox didn't isolate as much as I would like. It was a fun project but I still have the skipping problem. Short of hanging the TT from a wall shelf what can I do?