I was thinking you'd want to insulate the item in the can from the can itself and started thinking about that rubberizing stuff you can dip screwdriver handles in to shield yourself from electricity. I'm sure that stuff can be painted on with a heavy duty brush, the spray bed liner would be a whole lot easier to use though. Rubberized undercoating might work also.Static-Bags are actually "Anti Static Bags." They are a soft plastic bag that you usually get electronics in. They are either a light pink or silvery metallic looking bag. As thin as they are, they work GREAT - as long as there is no hole. A tiny pinhole can render them useless.
Amazon.com: Antistatic Bags, Resealable, 6X10, 10 Pack: Computers & Accessories
I would still line the ammo can with something non-conductive. The hardware stores sell truck bed lining in spray cans. It is pretty good stuff for a wide array of projects that have nothing to do with a truck bed.