Filters are available at any auto wholesale outlet, or any heavy truck dealership ----BUT ------ I have done this over the years, and I have refined this in later years.
If you are doing high mileage, and returning to your own shop regularly, it might be (is) worthwhile to develop your own support system.
But, a motorhome generally is not a high mileage unit.
I find my oil change intervals happen when I am in NY or CA or Dawson Creek BC, and I am not going to carry the gear to do that on the road.
Take you Diesel Pusher to any Heavy Truck Shop and relax with a coffee while they do a professional job, quick and clean.
The shop time consumer is greasing your unit. If you want to save the shop hour rate, grease your own unit. You can carry that air or battery powered grease gun, and you know you have got all the grease fittings. It also gives you a chance to inspect the dark side of your motorhome. I grease my CLIPPER every 2500 miles. (approx.)
When I go to the truck shop, I specify an "ENGINE OIL CHANGE" and a "COOLANT DCA READING" only, and find the cost makes economic sense.
If the coolant DCA is low, you then buy and change the 'charged' coolant filter at your convenience.
"LOVE and LOSS, are two of the greatest emotions one can experience. -- I went to school to learn about "WHAT GOES UP MUST COME DOWN" but I had to live my life to learn the lesson of: 'WITH LOVE THERE WILL BE SORROW'."
David Stewart. (after loosing my NAVIGATOR)