Headset protection on road bike
 

I have a Cannondale R800 road bike. The place where the bottom of the headtube meets the fork seems very, very vulnerable to grit and water getting in. I mean both the open end of the steerer tube, and especially the small gap between the top of the fork and the bottom of the headtube. This gets full of water and grit on almost every ride, it's difficult to clean, and I'm worried that this will damage the headset very quickly. Is there anything I can do to protect this?

I think it's best to leave well enough alone.

The open hole that you see is just a hole. The bearings are on the other side of the tube. Keep in mind that the hole also lets the water out so that it can dry between rain rides. In fact, I'm a believer in having a drain hole in the bottom of the bottom bracket shell.

So what about the headset bearings? That's the part that really needs protecting isn't it? Not to worry. All of the average and better quality headsets today have seals that prevent water from getting into the bearings. As long as you are careful not to damage the seal whenever you install a fork, you'll be fine.

This has been covered extensively in this forum before, so if you search you will find alot. One simple (and cheap) trick is to cut two sections from an old tube. They need to be about 1.5", or maybe a little less, in length. The only trick is that you need to have the fork removed to install the bottom seal and either your bars or stem have to be removed to install the top seal. These will also protect your headset seals from getting the grease (air_and_roadgrit) blasted if you mount your bike on a car top rack.

Try searching on "headset seals" for more.

Lizard Skins makes a neoprane headset seal with velcro to attach to the lower headset race. There is a downside to using an inner tube: it will quickly degrade in warmer weather.

Yes, I'm sure that's true. But, do you think that neoprene does not degrade in the same conditions?
I have been diving for over twenty years now and the worst thing for neoprene wetsuits is the sun.
So, the point is that there is no perfect solution. If you are servicing your headset at some resonable interval, then you can replace the homemade seals with new ones (which are "almost" free). I have been using seals made from one tube for over five years now and I'm still on the same tube (got about another foot to go). I service my headset twice a year and always replace the seals - which, btw have always looked fine. I'm pretty sure that most of us will always have an expired tube around ;)