Rather than tell you what I do, here is the answer to your question. From the Cummins RV generator handbook. โYou should change the engine crankcase oil after the first 20 hours of operation, and every 100 to 150 hours thereafter. โ https://power.cummins.com/sites/default/files/literature/rv/F-1123-EN.pdf
I believe the owners manual will advise as to the correct Oil Change interval. Ours is a 5500 and the interval is at least 150 hours. Make sure you follow the recommended interval and use the recommended oil grade. Don't forget to change the filter each time as well. Our oil grade is 15W40 as recommended for the North American climate.
I never hit 100 hours per year so I change yearly...usually early spring time when I am also taking it out of its winter hibernation. There is no oil filter, just a simple drain-and-replace.
'17 F350 STX 6.7 '15 Stealth WA2313 '20 Can Am Maverick Sport 1000R