I had the same issue with the Grenadier. I previously had a TruckVault in the bed of my Tacoma for my long guns and other gear, and it worked very well. I tried repeatedly to speak with someone—anyone—at TruckVault, but they simply did not respond.
I looked for other solutions, but none satisfied me, and ultimately I compromised. I purchased the Buzz Overland side-by-side drawers, drilled one, and added a high-security Medeco cam lock. The Buzz Overland drawers have a lip on the top edge that allows for the installation of a cam lock.
The side-by-side configuration does not allow me to store a long gun (the compromise), but I am able to store other types of equipment. Overall, I am content with the purchase and modification. What I particularly like about the Buzz drawers is the ability to add additional Buzz systems if desired.
As one forum member mentioned, Black Sheep offers an under-seat safe. I purchased one, installed it, and replaced the lock with a high-security Medeco cam lock (keyed the same as the other Medeco locks). Happy with the purchase.
Hope this helps, and good luck.