Here's the issue. As said these manuals do not exist for most RV manufactures. Winnebago is the exception for at least their DP motorhomes. Most manufacturers don't have them so they can't be held accountable for discrepancies and variances during the build process. In many/most cases wiring is done by the "plan" in the assembler's mind that showed up that day. So if the same persons is there for a while then there may be some similarities from one RV to the next. Have someone else come in and their plan may be different how and where they run some electric lines or plumbing. For most builds you can expect the minimal amount if effort and materials used. After all since they work and are paid by the job, the faster, read that least effort, the sooner they are out to go to their farm, or bar, and do something else. Is that a cynical commentary, yes but unfortunately a pretty true picture how it's done. The QA doesn't establish firm and specific procedures therefore no meaningful QC exists.