Unless you are driving on gravel/dirt roads all day/everyday, I suspect these filters will last a "life-time" in an RV [before the indicator tells you to replace it]. I have changed every 30K and thats based on peace of mind, not dirt content. If it makes you feel good--do it--but dont think I'd carry a spare around.
PS--there is an alignment cone-shaped bracket at the rear of the filter compartment. Make sure the openning on your new filter matches the old filter/fits over that cone. A slightly smaller diameter openning will cause the filter not to seal and is a disaster for yr engine. [Read thread on "dusted" engines.]
2003 Alpine 40' MDTS
New Braunfels, Texas