I have an ISX12 in on a Spartan K3 chassis. Cummins documentation says that if the ISX12 is installed in a MH, that the oil needs to be changed every 6 MONTHS. I confirm this with Cummins via email. I did that once and now change it yearly based on 10K miles/year.
As far as the setup to change your own oil, it’s not that bad. When I still had a S&B, I change my own oil. I had the oil plug replaced (during oil change at Speedco) with a valve and when changing the oil, I would air up the coach to maximum height. I believe I could get a 5 gallon bucket under the coach, but I opted for a 3 gallon bucket. I would open the valve, fill the bucket, and then close the valve. I would then pour the 3 gallon bucket of oil into 5 gallons buckets. I would put the lid on the buckets and then take them to the landfill which had oil recycling tanks. It was 5 miles away.
Yes it’s more work to change it yourself, but I prefer doing things myself. I know it is done right, oil filter changed, etc.
Also being under the coach it gives me the opportunity to check things out for any issues that may exist.