If you spend a significant amount of your time offrading, and especially if offroading in dusty or dry conditions, I would reccomend you not use a K&N airfilter, period. A dry genuine filter will trap particulates smaller than 400 grain fineness, however a K&N will pass particulates larger than 200 fineness.
A K&N filter must be, as you already know, oiled, like the old time air filters. In dry and dusty conditions, the oiled element will become plugged very quickly, and the dust will become oily as well, sticking to the element. A dry element can become covered in dry and dusty conditions, but when the engine is shutdown, a significant amount will dropp away from the element.
I know lots of people love their K&N filters, and some so much so as to say that they get an increase in power (Isaac Newton would argue against that succesfully, and he never heard of an internal combustion engine). All of that notwithstanding, they are a poor choice for any regular offroading.