I just sat mine on sorbethane feet.
Every TT I've had was sensitive to what it sat on. I wouldn't use spikes because they couple the deck to the supporting structure.
The car body damping panels were something like this https://www.ebay.co.uk/p/Silent-Coat...d=161282941044
I will post some photos of the underside of the Systemdek.
Might take a day or two ......