rg, most diesel MHs have two fuel filters, a primary and a secondary. The primary is normally located off the engine and has the water separator unit and drain as part of it. The secondary fuel filter is normally attached to the motor. Your owners manual should cover the location of the water separator unit and if not you should contact the dealer you bought it from or Monaco tech.
"Gunner" USN Retired, Airdale
2004 Monaco Signature 44' Conquest. Detroit 60