Its only my thoughts and opinion on this. As you did not mention the brand it leaves us kind of up in the air. So if I understand your post you are in need of replacing the wireharnes that was damaged. Now there are multitude of wireharnes in your unit for alot of different things. Some more important than others. The factor repair folks may have a better idea on how to fix that. But on the other hand the "whole" harness is not damaged just replace the section of wires. Your local shop can do that. Is there other items that need replace along with the wireharness. Those items can be ordered from any repair shop.
As for Camping World each one is different. I had work done from the one in Cedar Falls Iowa and was very pleased. I think no matter who you take it to large or small plan on not having your rig for along time.
I live where we only have a small rv shop, I would trust them far more than larger shops. But thats something you will have to decided. I would make a few road trips (car) visit and talk with everybody about the problems and get their feed back. Take pictures of problem with you to show.
I had a fire in the front of our DP last year that melted most of the insulation off the wires, plus a few other parts. I did not replace the whole harness just the wire. Reason I said that is your smaller shop may be a little more concerned on making it right.
Good Luck
Itasca Meridian SE 36g
Road Master Tow Dolly