1. aftermarket air box with outerwears "lid" mounted (Velcro)
2. stock airbox with snorkel tubes and an EHS Racing lid
as mentioned only use foam filters with the added protection of an outerwear on it.
EHS Racing lid:

I use the EHS racing lid. Works like a charm. Went on a super dusty ride last year and there a $.50 piece size dirt mark on my Uni. Prior to using this lid, I used the furnace filter element over the top of the stock airbox. Didn't notice any power loss with the EHS setup. I also use a closed airbox, no snorkel with NAC's covers.