I always love the oil change and selection posts. Almost like religion and politics. I do not really even know where to begin but I'll throw some thoughts out there. Now, keep in mind that I have 40 years' experience with larger industrial engines being used for emergency power and fire water pumping. Limited use equipment that for most part is only used for testing, running for some maintenance, and sometimes really needed. At one time we used some of the generators for load shedding and power assist but the environmentalist put a stop to that. Anyway, for these engines there are requirements for maintenance and validation.
As for annual oil changes there are some factors that may dictate that. Oil itself does not go bad in a year. What does go bad is the filters, oil, fuel, and air. Even the better ones there is some cellulose base and once wetted, they begin to age. Having an oil or fuel filter separate and pass the media into the fuel or engine lubrication system will make for a bad day. BTDT. How long will they last with intermittent use? As moved to synthetics and oil testing, we eventually moved to annual filter replacement. OK for the filter spiel.
Comparing the care, oil changes whatever from these Diesel engines to our car or light truck experiences, you really can't. Not even close. As for cost effectiveness. Most of us have been frugal driving older, cheaper cars and how we saved enough coin to get into the RV world. While you may never see an engine just plain wear out form lack of oil changes, cheap filters, wrong oil, they can and will fail along with some of the support systems including turbos and the fuel injection system, injectors. Traveling away from home, the past decisions can lead to $20K to $50K roadside repair events. Most of our Diesel pushers have 100 to 200 gallon fuel tank. $500 to $1,200. Driving is around $1/mile just for fuel. Why even question an annual oil and filter change? The wash and detail guy gets me $700 for a wash and quick wax.
The only way to know how often oil really needs to be changed is to do testing. And still there is a lot of stuff that does not show up in the testing. The really small particles. As for recommended oil change intervals, oil and filter selection, the OEM goal is not ultimate engine life. Part of the recommendations are to promote reduced ownership costs, regulatory reductions in consumption, and just getting through warranty. RV manufactures want to sell you a new RV, the chassis supplier wants to sell chassis to the RV manufacturers, and they also want to sell you parts and service including new turbos and engines. The promote longevity and reputation but they really want future and repeat sales. Think home appliances now.
Back to oil change frequency, the most important changes are when the engine is new. Get the bad stuff, machining debris, casting sand, break in materials out of there. Frequent changes the only way. Starting our engines during storage, not driving them is hard on the engine and the oil. Will show up in oil testing especially during break in. My Denali was after 15K miles for the high wear readings to stop.
Anyway, hope I gave few good ideas. Should anyone want some further help, oil and filter selection, let me know. Engine oil is more than just simple wear protection. Also give though to the other fluids such as transmission and hydraulics. Most all equipment failures come back to fluid system failures, one way or another. Now get your rig out there and use it and put miles on them faster than putting months on them.