If you have Direct at home, chances are you can to use your home receiver. If you travel far from home, you will have to contact Direct to change the local channel broadcast (and change it back again when you get home).
There may be some receivers that are not compatible with roof-mount dishes and I'm not up-to-date on what is currently out there.
Dome type dishes won't get specialty HD channels on Direct because they are on a satellite the dome cannot tune in, but the standard networks are all HD now anyways. Open face dishes can manage any of the Direct satellites. Both types are auto-seeking these days, so equally convenient.