Try filterbarn.com and compare prices, they sell fleetguard which is the brand cummins recommends. I don't like NAPA filters, personal choice. Now it's been about 10 years ago, but there was a great oil/air filter study done, and the OEM filters did a better job than any of the aftermarket ones, the exception was Purolator filters air and oil was as good as the OEM's for less money. I change the Air every other year. The coach never gets the 15k miles cummins say is the oil change miliage interval so that happens in the driveway every July along with the genset.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech