Karl, I don't recall if I've attached copies of our (2007 Journey 34SH/SE) owners manual, chassis maintenance manual, chassis operators manual etc., for you in the past. If not, sing out and I will.
To your immediate question, here's a quick reference guide with filter part numbers and so on.
CUMMINS ISB maintenance & operation.pdf
This refers you back to the chassis maintenance manual, which tells you approximately 5 gallons of 15-40.
About to start an on-line argument here, but I have always used Shell Rotella.
Fair Winds and Following Seas