Any useful tips for mud prep on these mini quads?

My main concern is the air filter getting wet. Last year at one of the races I saw what looked like 1/2 of a milk jug mounted over the filter on one of the kids quads. I wish I had taken a picture or paid more attention to the details... I don't see any great ways to mount one. Has anyone used the Hetrick air filter mug guard? It looks nice but at $185 I think the milk carton fits my budget a little better right now. Thoughts?