Garbage bins around small scale office/light industry parks are real good places to score high density foam pieces. Trimming discards are good finds for cases.
Grey or black high density foam pieces make excellent storage containers for handguns and/or magazines. If you want to tuck one up under the dashboard or seat of your car/pickup. The dark color almost insures that it won’t be noticed, even by mechanics.
Use a sharp knife to cut a slot SMALLER than whatever you wish to conceal. Tear out a 50% size chamber deep inside the foam to make room. Stretch the foam around the item. That will keep it from falling out. The position it using light wires or zip ties. Don’t block your access slot.