The following video highlights a very simple product available at Life View Outdoors that will keep you stuff dry, your gun safe for airline travel, or simply protect electronics or other things  while you are boating.  The price is very reasonalbe since you can use the Plano boxes for different things unlike a dedicated gun case.  If you decide to use it for a dedicated gun case, you might want to pick up some foam at at craft store to protect your gun.