I installed this, I've recently installed a 2nd next to it and likely will install a 3rd. These are the end-toolbox units from Harbor Freight. Yes, mostly they make junk, but their "US General" boxes are great and they are all I use in the shop now. They're ball bearing units that lock.
I keep the keys on a small chain that is connected to each box.
Basically, to hold them down, I build a little wooden frame, remove some of the lower drawers and connect the tool box to the frame, re-install drawers.