Welcome to the forum!
Did you call the customer service department at Thor? That would be the first place to start. There are several numbers that get you there, one is 877-855-2867.
You will likely find that there was no manual for the RV, just individual manual booklets for the appliances, furnace and water heater. You can probably search out all of those from the companies that manufactured them. You'll need the model and serial number from the units.
Only some of us learn by other people's mistakes, the rest have to be the other people!