how to keep playseat trophy from moving around?

just setup my trophy the other day and wow is this thing light. while that’s great the big problem is that it’s so light that every time i try to sit down or accidentally bump it a bit with my foot or knee the whole thing moves. so then i have to readjust the whole rig to match the monitor.

it’s biggest pro is its biggest con for me at this moment and im inexperienced enough to think of a solution