You are throwing your money away using synthetic in an RV. The advantage of synthetic over conventional oil is the time it takes to break down. Unlike semi drivers who are putting on 10s of thousands of miles a month, the typical RV driver will put on less than 5000 miles per year.
Your money is much better spent making sure that you change.the oil and filters at lease once per year ... just before putting it into storage for the year.
Also .... do not get fooled by names or brands .... many are rebrands of the identical oil.
This advice came to me from the director of quality at one of the major oil and gas firms her in Calgary.
Cummins has a hot line phone number, and a online forum direct to cummins HD i would contact them direct, all the issues my cousin had with his they were great to deal with and will tell all the specs and more so try them.
2010 Cedar Creek Silverback 35ts
2001 GMC 2500HD w/ Allison & 8.1