also, if you run your truck in very fine and dusty clay soils, be warned that these super fine particles will pass straight through any air filter. in australia, some of the particles are down to 2 microns in size (in places) and most dirt bike filters only trap particles above 5 microns. RC filters are no different, it depends on the type of foam used.
though, the finer the foam the more intake restriction you will get.

paper elements are ok if they are used with a oiled foam pre-filter. however i would recommend sticking with just oiled foam.