The Kings Highway is a very deluxe, all
fiberglass motorhome, at least the ones I have seen.
As far as manuals, all the RV manufacturers buy parts and components from the same short list of suppliers. So you can find manuals for the parts in your coach, even if the manuals are not from Kings Highway. If you want one just because, if you are patient, sometimes vintage manuals show up on eBay. I've bought manuals that way myself.
There are also quite a few vintage trailer clubs out there.