Just wanted to compile your ideas here. Have seen people use velcro, double sided tape, electrical tape, etc. to cover the hole underneath the chassis.

So what did you guys use? As for me, I might initially try the velcro way.

Fluffy velcro

Thanks. Mind sharing some pictures? Also, did you have to disassemble to front end to tape the velcro?

Neoprene. Cut from a beer cooler. Or wet suit would suffice. Thin stufff though.
Spongy/soft/smooth
I cut a cross slit, not a hole. The material is rather slippery for shaft to spin in so no extra drag etc.

http://youtu.be/3sfIymdh4Es?hd=1

A few layers of heatshrink around the shaft has worked well for me.

i used some electrical tape covered with shrink tube.

Mines still wide open lol since the day I got it back in 09. I do have the new longer clear cover though.

Never had any real issues with the opening, sure some stuff has gotten in there and scratched the center shaft which is why I deanodized it.

electrical tape n multiple layers of shrink tubing

I've tried covering that hole in the past with heat shrink, tape, fuzzy velcro....
In the end I always take it off
I've been running it like that for a while now and its going to stay that way
As long as you have a motor mount with an oversized bearing your fine
I'm running the king headz one