Forget the dome and have a Winegard Trav'ler installed. You can have either a Directv dish or Dish model installed and you will get HD without any problem. You can have a Joey/Hopper system or use the Genie system from Direct - either way, you will have HD, an HD DVR, and all the comforts of home. You can have as many tuners as you have TVs if you so desire. Can't do that with a dome.
If you are having your coach built, Tiffin will pre-wire for the Trav'ler for a $250 +/-. BTW, the DISH version installed should be around $1500, the Directv version a little more.