I suspect you will find that the hardware is already factory mounted on the inside since you would have to be a double-jointed monkey to install it after the wall was up. They just didn't do the cutout because it would have served no purpose in your case. A saber saw will take care of that problem. Take out the "radio" and reach in and down - at least that is where it is in mine.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.