I've done some work with the automatic ones (the ones which power on, determine where the satellites are and "lock on"). Those seem pretty cool.
They mount on top of the RV in a dome and the "dish" is inside. The dish is small and therefore actually moves when switching between satellites. The biggest downside is that moving parts are involved; but, they aren't moving far or a large percentage of the time. However, if someone is in the habit of constantly channel surfing, I could see where that would wear on the system.
John