I never really care for air box mods. IMO just take the lid off... there you have plenty of air. Then if it rains or is muddy.... just put the lid back on. And when winter comes.. and your bike runs leaner because of the cold... put the lid back on and it helps correct the jetting.
And when you run with your airbox off pull the drain plug, so if any water does get in it just drains out.
I modded an airbox lid before, on my Blaster. I had holes, then then I had holes with filters. It was just a waste of time. And I never had a complete airbox lid for if I did want to do some water or mud riding.
440, Ross 11.5:1 piston, Web cam 479 grind, race port & polish, oversized valves, hardened rockers, CRF450 cam chain, 39mm FCR carb, lightened Flywheel, Stock clutch, WB CDI box, K&N filter , WhiteBrothers E-Series full exhaust, Sidewinder Chain, 15/36 gearing, open airbox, LSR Axcaliber +3.5 axle, Houser Racing +2 a-arms, Elka triple rate, fully adjustable front shocks, +1.25 Houser swingarm, Tag Metals X5 bars, Arens +1 steering stem, Muscle steering dampener, Stainless Steel brakelines, HeatSeeker temp. guage, Pro Design kill switch, DG Pro Series nerfs, 8 run Hauler paddles. ~~http://www.sounddomain.com/id/trick440ex~~