Bob,
The last time we talked to DirecTV about it, you can pay a small fee(5ish dollars) to add an additional access card for a motorhome receiver. You can call them to activate and they'll only charge you the fee as long as you need it, when you park for the winter you can deactivate.
I don't know if this is still accurate, we last asked them a couple years ago.
Brad Jerew
Wild Times Motorsports
www.wildtimesmotorsports.com