You have excellent results using foam pads and slabs of concrete, and that’s fine, but there’s people who also have excellent results without.
I don’t use foam, rubber or concrete. All my printers sit on the same 18mm birch plywood table which is bolted into 2 walls (corner) which means it can’t move in either XY direction. My walls are my “slab of concrete” if you will, only much better. Zero vibration even with all printers running at full tilt.
There are industrial printers which can print with quality while sitting in the trunk of your car while you drive over a bumpy road, but they use closed loop motors and high precision ball screws instead of belts to ensure consistent relative motion (the only thing that matters is the motion of the nozzle relative to the bed), and they usually have a bulky steel frame.
Whatever floats your boat is the solution.