If you do go for solid tech, feet of silence under the rack for sure would help with isolation.
There's also the Townshend - seismic isolation stand?
Perhaps a better option is to get something you like, or BSR custom to something you like the look of on the internet, and put Townshend seismic corners under it?
I am having a two tier low level rack built for my system out of a metal frame and mesquite wood locally sourced. I have incorporated tuned mass on springs in my design. I am trying to keep it low, like when people place an amp on an isolation platform in front to not get in the way of speaker imaging - but also not have long cable runs.