Nice work but your engine shouldn't suck dirty air or dust if you have an effective air filter. At off road speeds you certainly won't benefit from any ram-air effect.
And it will be critical that you do avoid bad weather, because it won't be the rain, you'll have a problem with. It will be tire splash when you go try puddles and possible submersion if you have to drive thru deep water. If either should happen, you'll hydrolock the engine.
Honestly, the wheel well, fender area is a cleaner and drier place to draw air from. So long as you have a quality filter, any dust that blows into the engine compartment, will not get into the engine.
Ed