That may explain why he's working at Best Buy.
Digital either works or it doesn't - all you need to do is get enough signal to the set so the picture doesn't freeze up or pixelate. At that point the picture is it's as good as it's going to get.
Coax is rated in attenuation per foot, and the loss increases both with frequency and distance.
For satellite work, the distances we're talking about inside a motorhome make no real difference in using RG-6 over RG-59. Just make sure the existing wiring isn't going through a splitter or amplifier that will block the DC voltage from reaching the dish.
If you're running 50 or 100 ft. out to a tripod mounted dish, definitely use the better RG-6 outside the rig.
Over the air digital TV is lower in frequency than what comes out of the Dish, so it's even less sensitive to what kind of cable you have in the walls.