For strength and corrosion resistance why not get Grade 8 (or F911) hardware and have it hard chrome or electroless nickel plated?
Chrome plating would lead directly to hydrogen embrittlement unless the plater knows exactly what they're doing and does a bake-out within a very short time span of them coming out of the chrome bath. There's a Mil-Spec for baking out hardware after any type of electrolytic plating process out there somewhere if someone wants to do this.
Electro-less nickel can peel if you're not careful in choice of the plater. Ask any electro-less nickel plated Series 70 Colt owner. A good choice for electroless nickel-teflon would be Robar's NP3. Cal-Tech Plating is a mil-spec plating house that also does this process and straight electroless nickel, but they are strongly NOT recommended. Nickel-teflon is an awesome plating for corrosion resistance and dry lubrication, but your torque specs will need a radical reduction and don't expect self-locking nuts to still work that way.
Foremost states that their F911 bolts are made from 8620 alloy, so whatever environmental limitations 8620 has will apply.
I know of a robotics firm that had an unexpected failure of a pivot pin made from 17-4 H900. In air it is 200 ksi tensile strength with surprising ductility. This material makes a phenomenal bolt that will last weeks on a high volume production tombstone where a Grade 8 bolt in the same place wouldn't even last one shift.
10,000 feet down in the ocean it is not the same, the material experiences brittle failures in cold, saline environments. Something not well documented about 17-4. So could have the bolts made from 17-4 H900 so long as you don't plan on making your Bronco a submarine.