Awhile back I purchased a Mossberg 500 Just in Case Mariner 12 gauge shotgun, which came already housed inside a very thick resealable 10-mils thick Visqueen bag, in its own Schedule 40 PVC tube, which is designed to be waterproof down to 40 feet below water surface.
It also came with a survival knife and a multi-tool, which were not of very high quality, but I tossed them in my tackle box anyway....
The PVC tube is designed to float, and comes with an attached nylon strap shoulder sling, so you can take it onto your boat, and if it goes under, your shotgun will not sink beneath the waves....
It is also designed to survive being buried. It comes with a resealable rubber donut ring, clamped by zinc coated steel plates, and stainless steel hardware (carriage bolt and large wing nut) so you can access the contents without tools in an emergency situation (hey, stuff happens).
The Mariner is nickel plated, so it is designed to withstand rust and corrosion, and exposure to humidity and moisture - it makes a perfect truck gun, or trunk gun, as the case may be, as a result.
18" barrel, seven shot IIRC, and although it has a pistol grip, it makes a nice breaching tool, and would suffice in an emergency until you could find something better to shoot with.
These shotties have really jumped in price since I bought mine (pre-panic) but it is a very solid and well-built shotgun, and would be very useful in an emergency or SHTF situation, or as a breacher, or boat gun.
Since it was capable of serving multiple roles I needed (it fits on the front rack of an ATV in a tool holder with rubber snubbers like it was made for it), I decided to buy it, and now I am very glad I did.
I like that it floats, you could bury it if you were so inclined, and you can carry it with you and not worry about it getting beat up on the trip (plus the tube is good for storing handheld electronic stuff you don't want getting wet).
All in all, a very versatile prepper's weapon, and a decent hard storage design option to keep it out of the elements, if you hit the outdoors hard.
A picture is worth a thousand words, as we all know, so here you go, offered up for your viewing pleasure:
