Go write down make and model of all the appliances. Then go online to the various web sites and download the manuals there. RV owners manuals are nothing like car manuals and basically are not worth the paper there printed on.
As the other poster said for all appliances. even entry steps there are manuals you can likelyh download Just google something like Dometic RV123123341 Manual (NOTE that's not a valid Dometic model number)
One caution.. if you get an DOMETIC Microwave... Might be an LG (Same model number however) or another make.
Same for furnace, Water heater and .. Well everythign save floor, walls, roof and ceiling.
There are two books
The RV owner's handbook
The RV Book
Get whichever one your local RV dealer or camping world carries (one is a Woodalls/Good Sam publication so CW has it.. Both are rather close to the same. Do either one is good.)
Generic "Owner's manuals" for most RV's Some chapters you can ignore.
Almost surely won't be worth the effort to find it. Lack of detail and covers multiple models & layouts. But you can give it a shot - just Google '1998 Thor Comfort manual" and see if you get a hit. Thor has some manuals on their website too, but they seem to be only motorhomes.
What they give you is a folder with individual owner's manuals of the individual appliances for most of the appliances and installed parts. A/C, range/oven, furnace, fridge, and maybe others like water pump, toilets etc, but don't count on it. There is no manual to tell you how the camper is built and how to operate it. Manufacturers just makes way too many models and changes year to year to bother with such trivial information. You have to get the seller to try to tell you how to operate it, though a salesman knows little, or read each individual owner's manual or search the forum for the info you are looking for such as the 100 others who have asked the same question and gotten the same answer.
Use the Search function. it is an icon that looks like a magnifying glass. just type in search words and you will get a list of forum post that are what you are going to ask anyway.