This one time, at band camp, I rode in a dusty area (the really fine silt type) with my airbox lid off. I thought for sure my new gauze type filter would be alright with its cute little prefilter thingy on. When I got back to the truck, I pulled off the seat to make a quick check and... oh the horror!
Vibration made the prefilter start to work its way off the filter, it was only half-way on. Dust had built up on the filter, but not underneath the half that was still covered. I'm telling you, the difference was night and day! I was so worried, I changed my oil right after cleaning the filter.
anyway, there's this ebay seller, his username is
xcbob. He has this outerwears cover that is cut to match your airbox and is held on with velcro. The velcro is not too secure, so get creative with it. I forget how much it is, but it is a cheaper alternative to the other lids out there.