I use the car equivalency theory. 1 hour at 50mph. So, for oil, 6000 miles to 7500 miles is not unreasonable. That's around 120 to 150 hours. Fuel filters are a bit of a crap shoot because you can't predict fuel quality .... 15000 miles equivalent would be around 300 hours. Time can be a factor but my genset gets used.
2005 Newmar Essex 4502, 2013 Caddy SRX
1997 HR Endeavor 37, CAT, 1996 Geo Tracker