Dennis-
We all thought the CB connectors were under the dash of our '06 Monterey. Eventually the tech at Bend found them tucked away behind the driver's arm rest, where most of the switches, parking brake, tranny panel, and etc. are. As I recall, the upholstered side of the "armrest" can be unscrewed and removed for access to the menagerie of things behind it. If you couldn't find the Unified Tow Brake harness under the dash, try looking under the "armrest".
We went with a Roadmaster Brakemaster system, which I really like, and the huge new Roadmaster headquarters/facility is now located near us in Vancouver, WA, where I've had excellent service solving special problems. But you are correct in that our coaches are supposed to have been ready to go for a Unified Tow Brake installation if that's your preferred route.