When washing the salt off your bike, make sure to clean the inside of the steerer tube. I had a fork with a steel steerer and it really pitted up in a few spots. The pits were deep and large enough that I was concerned the steerer tube was going to start to crack.

Many of the higher strength steels are less resistant to corrosion than ordinary hi-ten.

When I put in a new fork, I used some leftover rustoleum to coat the inside of the steer tube.

Most steerers I have seen were open to the elements even if you run a fender.