Northeast cold weather semi auto shotgun lubricant of choice and why?  Ready go!

ATF , yup, auto matic  transmission fluid.

Benelli oil

I got tired of paying the premium for "gun"cleaners and lubricants. I found the old recipe for Ed's Red. ATF, various distillates to thin out and lanolin for rust resistance and your hands. I substitute Coleman lantern fuel (heptane) for the turpentine, mineral spirits and acetone. It won't remove copper fouling but it cleans and lubricates. ATF has to work at high and low temps, extreme pressure in the gears and not damage synthetic seals. And it's not $hundreds per quart like gun specific products.

Why not use CLP?

As mentioned, Eds Red in a 5 oz Ronsonal lighter fluid container tucked into the blind bag.
This is for a 930 Mossberg and 1100 used on sandbars and lay out boat hunting on the Great lakes.
Never had any exposure to salt water, so I can't comment on it.

I use a very light application of FP-10 after cleaning.
For in field high volume cleaning/lube i keep a can of CLP in the blind bag.  Those mornings where you're shooting into a ton of snow geese the gun tends to need a shot of CLP here and there.