managed to pick up a tufloc shotgun lock off ebay for almost nothing - if you arent familiar with them - thats what most law enforcement uses to mount their remington 870 in a patrol vehicle - crown vic trunk lid, divider cage, etc.
It locks around the pump tube/barrel with an electromechanical lock - theres a button hidden somewhere, hit the button, the lock pops and you can grab the gun and go - also has a manual keylock that uses a handcuff key.
Anyway, sometimes when I'm out I'll carry the 12g in case I see pigs or whatever and i wanted a secure way to carry one - with a couple of minor mods, this worked out great.
first problem is this was made for a remington 870 and I wanted to use it for my maverick 88 - same thing as a mossberg 500.
to fit into the lock, I shortened the foregrip on the pump a couple of inches, with a mossberg - the pump actually overlaps the receiver a bit at full pump, so the foregrip is longer than most.
then found a mounting spot next to the back seat.
had to do a little bending to the mounting plate to make it clear the tac flashlight mounted under the barrel then made mounting brackets and bolted it in.
still need to pick up a momentary switch to hide for the release but at least its mounted.
anyway - it hides pretty good even with the windows out thanks to the nets and the pack mounted to them
- here are the pics.