The maintenance schedule should be in the Ford manual that came with the RV.
We obtained all the manuals for our 2005 Spirit by downloading from Ford, Winnebago, and the various equipment suppliers respectively. While on the Winnebago site, make sure that you also get the wiring diagrams for the coach as well. They will come in handy for troubleshooting issues that come up. Onan, Norcold, Dometic, Suburban, Atwood etc. all have service manuals available for their equipment as well as the owner's manuals.
2005 Itasca Spirit 24V