I wouldn't worry too much about protecting your gear with a bag while it's on the rack. The lift lines are WAY more abusive to your board than it being out in the open air while driving to/from the hill. If you ride park at all, then you should view your equipment as relatively disposable. If you're getting more than a season or two out of your board, then I imagine you're riding less than 20 days a year.
As for road salt, I just rinse my boards off when I get home, or at least wipe down the base and edges.