Bike Cover for Use On Car Hitch Transport

I am trying to avoid soaking my bike in a rainstorm when travelling via car.
I have a Performance Flatbed Hitch Car Rack so the bike can be completely
covered. The car rack arms do not go through the center of the frame, the
bike sits on a flatbed and is held in place from the top.

Do you have any suggestions for a transport cover?

Also, will using a transport cover be bad for the bike or anything? It
seems like it would increase the wind resistance so much that at 70 MPH
behind a car, it could damage the bike. What do you think?

I asked at the bike shop, and was advised against it. They said that no cover
made would withstand the wind. (?)

Instead, I was told to use a paraffin based
lube oil, and to "flood" the chain, rings, sprockets, cassette openings , and
any other raw metal part.

The worst part of a hitch type rack in the rain is all of the grit that flies
up behind the vehicle when on the highway.

It didn't seem to hurt my bike, the lube came off pretty clean with the
wipedown.

RRon