I believe there are stock locations, street side, upper cabinet, front in the 19 and amidships on the 21. Second location your choice since you are paying extra for it. There are standard locations for both electric, 120v and 12v outlets and cable and schematics available. My only change to the stock was changing 120v outlet to 12v outlet since i always go with a 12v tv.
Sometime life gets in the way of living.......