My father in law used to have a hunting lease down in Mexico years ago. He and a couple of other guys would hunt several times a year down there. Instead of taking the chance that some crooked fedarali liked he and his friend’s hunting rifles more than they did, they took a bed with a hidden gun rack in it. The side rails of the bed frame had grooves along the inside. Both groves were parallel the whole length of the side rail about 3 inches apart. When the bed was assembled plywood was inserted in the grooves creating a support for the mattres and a false bottom. They stored there guns in this space and left them at camp when they went home. Now this wouldn’t work for fast deployment because you had to disassemble the bed to get them out but unless you knew they were there they would be difficult to find. You could use straps or foam cutouts to hold the guns in place if the bed folds into the wall.