That's basically how my HR is set up, the engine mounted filter removed by coach builder and installed both primary and secondary filters in the back of the coach for easier replacement.
On mine, the primary is I think 20um with a sediment bowl and the secondary is 10um and has a water sensor.
Don't know why but previous owner on mine had put a different brand and part # 10um primary filter without a sediment bowl, maybe cost or availability. My owners manual does not specify the micron rating for the filters, just the Fleetguard part #'s and Fleetguard does not think this is important enough to put in the Spec table and really need to search for that info.
Someone more knowledgeable on your coach needs to confirm the secondary filter part number but the 2004 Cayman owners manual I found on line says the secondary is FS19596.
2004 Holiday Rambler Imperial 40PKD, Cummins ISL 400