I'm not sure on what to spray on them to keep that area from rusting.
Mud hides it well though.
You'll have to see what works best for you. I'd start with the on road settings first. Try what I have mine listed at and see if you like it. Loosen them up all the way, tighten them down all the way, and you'll find that happy medium. I leave mine at the same setting all the time.