Like most of us that purchased a truck without the factory brake controller, I had been looking for something that worked well but looked good. I ran across the Redarc Tow-Pro Elite while searching for a suitable unit. It is on the pricey side but was easy to install, looks good and has very good reviews. Since I just finished the install, I have not pulled with it yet. The controller (adjuster/switch) was installed in the headlight switch dash panel. There are two places that look like it wold fit, I chose a spot just below the credit card slot. Be careful when fitting the switch as there is not much room for error. The controller box was mounted on the inside of the panel below the steering wheel. That actual control box can be hard mounted anywhere that the two connections can reach. There is only a couple ways to fit it on this panel and it not interfere with wiring or othe structure. I used a little double side tape to mount and test fit the unit. Once everything fit, I then drilled into the metal panel ribs and installed a few screws. I used the factory harness adapter that was supplied with the truck, and soldered it to the Redarc harness. If you don't want to make your harness, etrailer has one already made up for our trucks for under $20. The best price that I found for this unit was on etrailer.com
Hope this helps someone and maybe saves some internet search time.
2015 Silverado 1500 Z71