Well. with a DOME you won't get HD on DirecTV, no dome can do DirecHDTV.. Just so you know.. and where as I am not sure about Direc, Dish moved all their network (ABC,CBS and so on) to HD.
Now, you put your dome on the roof and run the cables (May already be there)
put in an "A/B" type switch box where you plan on putting the receiver (A goes to the Roof up Above and B to a ground block or blukhead connector down Below, Mine is on the Brake Bell crank Bracket... See how that works)
This is for hooking up a dish mounted on a tripod when you are parked, epically if under the evil signal eating tree as I am just now.
Call Direc. tell them you have a motor home, get transfered to KVH (i think)
Call again, same thing.
Call again and tell 'em if they transfer you to KVH one more time you are calling DISH.
From there.. it is easy.