If your rig only has a single exterior coax input it will usually lead to a splitter and as mentioned before the satellite signal must reach the receiver directly. Many rigs come with separate exterior coax inputs for cable and satellite tv making it easy to use a satellite signal from a tripod mounted set-up.
Currently available dome systems can not acquire HD content for Directv subscribers and 18" sat dish only delivers Directv programming from sat 101 which only contains SD channels, a mute point if you are unconcerned about viewing HD.
Our rig only has a single exterior coax input and I performed this
modification to the Winegard antenna amplifier/splitter and it allows us to connect our HD sat dish tripod setup to our HD receiver thereby enabling us to view every channel we have at home.
We use our HD receiver from our master bedroom, Directv will lease you a receiver for $7 a month although you may be able to purchase one for yourself, they will still charge the monthly access fee for that receiver.
Pointing the sat dish to acquire a sufficient signal is not overly difficult, but will require a bit of patience until you have mastered the technique. Once you get the routine down it takes just a few minutes to enjoy sat tv at the campsite.