Our 2007 coach had the trailer brake pre-wire but it took weeks to find it. Our 2004 did not have the pre-wire so I ran a new wire.
Monaco uses a tunnel down the center of the coach to run wires and hoses. The front access to the tunnel is behind the front axle in the center of the coach. Ours had some expanding foam on it. The rear tunnel access is just in front of the rear axle.
I used an electricians tape and pulled the wire a couple of compartments at a time until I reached the rear. I had to remove the basement ceiling cover on a couple of compartments to find my plumbers tape when it was hung up. This is usually a 2-person job unless you are an experienced electrician.
I used 12 gauge aircraft multi-strand wire as the original was 14. Some folks use 10 gauge.
I used a Tekonsha Prodigy brake controller on both coaches and it works well.
Post #19 has more detail: