Okay, I picked up a pair of magnetic lightbar mounts that I'll be modifying this weekend. The plan is to put an adel clamp on the lower structural bar towards the front of the rack, then bolt each one to the mag mount. The material of the mount is about 1/8" thick, and adel clamps tend towards being sturdy (I use them a lot in aviation projects), and the magnets on the mounts are ...robust is too weak a word. I almost pulled my toolbox over trying to remove them from on top of it.
It's a 54" wide roll chest. I THINK they will keep the front of the rack from wobbling....