I ride a KLR on long trips, but I don't know about the XR. But the KN filter for the KLR is totally unacceptable for long trips on dirt. It clogs with dust too easily. And my bike will not run.
I carry two spare preoiled foam filters. This can get me 3-4k miles whithout having to clean one. They can be scrunched up to less that a couple of cubic inches each.
Cleaning them using gasolene in a plastic bag works pretty well too.
The prefilter sounds like a good idea too, but I have never tried it.