The Thor Owners Site should have all documentation related to your coach; including an all-inclusive schematics document for plumbing, wiring, construction, etc.
https://www.thormotorcoach.com/owners
If you have a newly designed / released model, there can be a delay for them to get the updated documents posted. However, Thor Customer Service should be able to provide them.
As far as following general best practices during assembly and formal QA / QC processes... it is correct they don't exist in the RV industry.
While the manufacturing line techs follow schematics, how they do their work will vary from one to the next. Some good... some decent... a lot bad. It is also assembled as inexpensively / cheaply as possible so things like conduit aren't used where most people would expect.
All you can do is go through your coach with a fine-tooth comb and fix, replace and upgrade the weaknesses if you have the capability to do so. Myself and many others on this forum do this day one of ownership.
Dealers won't do a better job than you. The only place that might do it right is Thor Factory Service Center in Wakarusa. I have used the Service Center for major warranty work but everything else I have improved myself.