Only one gun case for marine environment...
Pelican Case. Military tested and used hard cases for sensitive gear around the world.
Some other
soft case alternatives.
aLoksak waterproof soft bags. These are US Navy approved and guaranteed watertight to 200 ft. for two weeks constant submersion in salt water. But they are not as durable as the nylon canvas drybags listed below. They are heavy duty, for sure, but totally different materials are used.
Watershed Drybags. The best drybags you'll ever own. Watertight below 300 ft. submersion. I have the
Colorado Duffle and use it on all river trips. It is an incredibly large duffle at 31 inches long and holds a lot of gear. Good if you are bringing a long gun. Something smaller and more suited to handguns, cameras and other small stuff would be the
Ocoee.
Watershed drybags are also used by the Military, they have a complete line of
military bags as well. I did a lot of research on drybags before choosing watershed bags. As far as I'm concerned they are the best on the market and much better made than many of the other brands on the market.
I hope this helps with your quest of some of the best watertight storage bags and cases.