WD-40, Pam, or even a really good wax will work okay. I bought my plow new this summer, so I put some paint shield on it before the snow hit, in hopes that it would make the paint last longer... we'll see.
Keep it clean, painted and waxed. Right before plowing spray it with Pam and you will have no problem. Don't forget to power wash after the storm to remove the salt from the cracks and crevices of the truck and plow. Cheap insurance to keeping the rust gremlins away.