I use a cut up inter tube, to make a 3.0 inch rubber seal to put around the headset tube and
bearing area. It will keep some of the wet out of your bearing. I also had a couple of bikes
Ihad on a rack on top of the car. I found that a couple of time after, comming home from a
long trip to a bike ride, I would always tear down the bike to re-grease to bearing, that the
lower headset bearings would have most of the grease gone. After putting the innertube
around the headset bearing area, there would always be all the grease there. The only thing
I can guess was at 65-70 mph, the wind was somehow blowing the grease out. This is only
a guess.