Racked bike on long car trip: protection and maintenance?

I'll be heading west in my car with a bike on a back rack. The weather will probably be pretty crummy. I expect that a cover will block the rear view of the taillights, so the bike will be exposed.
The rear hub is "sealed", and the front is a dyno hub. The leather saddle will be off the bike.
What suggestions do you have to protect the parts and frame from close to 4k miles of weather?.