Have you actually examined the bearings? Are you sure the corrosion is the problem?? In any case, the solution to corroding bearings is the ceramic version of those. The ceramic bearings are often ridiculed in the cycling context, but they are a 'put them on and forget it' solution for the corrosion.
Yes, I’ve seen them after my bike shop guy pulls them, and they are nasty! I like the idea of the ceramic bearings, does Trek sell them or do I have to find the right size on my own? Also, are they a lot more expensive than the steel ones? I think I paid $49 for the last bearing.