There were a couple guys at Tanner a few months ago selling a thing that pushed under the mattress and came up the side of the bed with a "dowel" that the barrel of the pistol slides on to keep a pistol tucked tight against the mattress.

I didn't buy one at the show, and thought about it and was going to buy one at the next show, but they haven't been back. I tried making something similar myself and it didn't come out very good.

so for now, a pistol grip mossy 500 sits behind a bedpost