Having been into the electrical system of my 2011 Seville this year, I'd be really surprised that even if you had a diagram, that the person(s) putting the camper together actually followed it. I do believe that they have a pre-cut harness but from what I see, there is a fair bit of daisy chain circuits in there. I'd be reluctant to just arbitrary cut into stuff.
If you don't mind me asking, what are you wanting to do or is this for "just in case" documentation (also a great idea).
Al & Linda
2013 GMC Denali 3500HD SRW, Crew Cab, Std bed, 6.6L Duramax, Allisons, PullRite Superglide, Triglide
2011 Crossroads Seville VF35CK11