I had a HR24 receiver at home with a Slimline 5 dish with HD TV and a in motion dual LNB SD dish in the rig. Moved the receiver to the rig - SD worked great. Then one dark day in Oregon we could not get SD to watch the Olympics because in some areas of the country DTV transmits HD only. Upgraded the rig to a SWM dish (which the HR24 supports) and now had HD because of the rigs 720 TV.
Since then we upgraded the house dish to SWM and HR44 which is SWM only. Since we don't watch TV in the rigs bedroom that TV is OTA or DVD only. If I was going to upgrade the bedroom TV it would be similar Big Katunas post.
Keep in mind that DTV is not in the business of running HDMI or component/composite to remote TVs. Single coax to remote TVs using SWM and Genie Clients for each TV and of course there is a charge for each Genie Client. So you won't get much/any help from DTV for a RV.