Oil Change

I do not know the proper miles,time etc. when to change the oil, but we do it once a year or about 5000 miles. I know that it isn't many miles but when the camper just sits with changing temps. I do not want any thing to go bad with the oil. We also change the fuel filters at that time. I figure that oil and filters are cheaper than some kind of breakdown.
Just my opinion
Our engine is a Cummins 325
Bill