When I ordered for my house, I have the genie (thats what they now call it) and two HD boxes. I then added two SD only boxes. They came out and installed everthing on SWM at the house and activated the SD boxes as well as the rest of the system. I then removed them from the house, took them to the RV. Setup my dual LNB dish, connected them to the boxes, went into setup and changed it to the proper settings. Aimed my dish and enjoyed my programming without any thing complicated in the RV.
It is no issue at all.
If you want to order HD at the house and move them to the RV for travel, that you can do as well. You just need to go into the programming and set them to the proper LNB configuration without any need to deal with SWM.