Most of the appliance manuals are available on the manufacturer's web sites. Most often found in the "support" areas.
Try
Service Documents for service manuals for most major appliances (fridge, water heater, furnace, etc.). You will need to know the make and model number of your appliance.
You might also try contacting your motor home manufacturer to see if they can supply copies of the original owner's manual for you.
Don't hesitate to ask any specific questions you might have. I am not familiar with your specific rig, but there will be many on here that are. Remember we all started where you are at one time.