Haven't had the need to so far. Keep in mind. I've done the cannonball run style of trips when I've gone from my place to Tom's. Only stopping for gas/piss breaks. So it's not like they've been out of my sight. And once at Tom's, I'll unload the rifles overnight before we head out into the desert the following day.
Locally, keep in mind that I'm a hermit, and that I don't go anywhere except to work and back for the most part. So I never have the need to transport a box of that size. Maybe only a couple rifles that get tossed in the back, at the most.
No $hit right? The typical load-out that I've jammed into one of these to do the AZ run :
MRAD, AR-10 SSASS, AR-10 carbine, AR-10 SBR, DD MK-18, 300 BLK SBR. Plus a couple of pistols. Plus 4 suppressors, various optics and other things like bipods for different rifles (usually stowed with it's rifle in it's bag). And, all of the mags for all of the weapons.
Plus, I've usually brought at least one other rifle (s) as an off-shoot to show that I do have other interest's outside of AR's
As Tom said above. You load all of this $hit into one of these boxes, and they're pretty tough to move. And like I said before, if you wanted to, you could start with a layer of ammo cans in the bottom to add even more weight to them. You won't move these without the help of a forklift.