I can't speak as intelligently as some on this subject but I can tell you that since you are speaking of Direct TV....be very careful what you purchase for a Carryout System. As you probably already know, Direct TV has some changes coming down the pike. Thus, only certain receivers, at some point will be necessary in order to get signals from the 101 Satellite.
Its going to be very confusing so rather than going into it, I will say this, I've had Direct TV for 20 years and have used Direct TV in the RV via a Roof Dome, a roof mounted non dome and a portable Dish. When this change occurs, only certain receivers would allow me to continue using the three dishes mentioned BUT these receivers are not so easily obtainable. Long story short, I'm giving up on Direct at least in the RV for now. I will switch over to Dish Network (home and RV) sometime in the near future.
I'm sure someone will come along and explain this much better than I!!!