Welcome to IRV2.com, Irene.
Try ebay, but don't expect much even if you find the one for your make and model. The manufacturers manual is rarely more than an overview and some tips on RVing. Maybe a few things on the instrument panel of a motorhome.
RVs come with SETS of manuals - one for each appliance and the major components. There would have been a Chevy manual for the basic vehicle stuff, a stove/oven manual, water heater manual, furnace manual, tv manual (if factory equipped), water pump manual, etc. Many of these you can find online or you can copy one from another RVers who has the same model of appliance.
So, make a list of the make and model of each major appliance and start hunting manuals online and through friends and on sites such as this. Do the same for your Chevy chassis - figure out which one it is (Class C's are built on van cutaway or pick-up chassis) and then look for owners or service manuals for that - ebay is a good source for them.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL