Noah,,,,I highly disagree with you and your suggestion of using "Hot soapy water" on firearms. Would you wash out the inside of you vehicle's engine with water too???? NO.
That's like some dumb Marine corps DI's that have made the "boots" take their M-16's in the showers with them for cleaning. Uterly ridiculous!
Or the old claim that one could take a "SIG" or Glock in the dishwasher. Guns are guns, not "dishes" for cryn out loud.
Use a petroleum based product to DISPEL water. Some good products to use on the Remington Marine Magnum shotgun would be "RIG" grease, which can be applied lightly with a finger. CorrosionX as others have mentioned works great too.
Or...
Use "Breakfree Collector", which is a preservative only product, which has been tested by the military for salt water conditions. Stuff works great in the ocean. I use it on my boat in the pacific ocean, for all my long guns. Never once experienced rust.
Lastly, if one is really concerned about the finish, check out Robar's "NP3" finish. It tougher than any hard chroming job and is virtually impervious to salt water. I have the finish on two semi auto's I own and have gone completely in the salt water drink with the guns. I've neglected the guns for days while on the water and never had the gun's finish rust or blemish. Great finish, yet expensive. But it's worth every penny.