You can go for big bucks...or not big bucks. For a rooftop unit, $1400 or more, maybe plus installation. Or...the cheap way...(like me) tripod,dish, strength meter, and compass. Maybe 100 bucks
There are advantages and disadvantages to both. For the roof-top, if you're under trees...forget it. Maintainance? O, boy. And...according to quite a few posters here on the forum, rooftop (dome)system failure is commmon. Plus reports that if rain gets on the dome...no picture.
For the method I use...it can be time-consuming to aim the thing. And secure it from wind, etc.. But it works just the same. Good, clear reception.
I too have DirecTV in the house. 2 boxes. Hi Def in the living room...and SD in the bedroom. Not caring about Hi-def in the RV, I take the SD out of the bedroom and put that in the motorhome. Even so, i really don't use it all that much...especially for over-nighters. Mainly, when I know I'll be stopping for, say, more than a week...THEN I put up the dish. Otherwise, I use the cg cable system.
On the DirecTV website, there is a page for aiming the dish. Just type in the area code and the specs are there.
No need to ask for problems...tell DirecTV nothing, but pay your bill on time. However, some folks want extra East-West feeds....and other options. Up to you.
I have a passive switchbox...a great item to have...making switching from cable to antenna to satellite to DVD player a simple push of a botton.
G'luck!