I can not tell you what to order, I will let others do that but I can tell you this.
MAKE SURE YOU GET AN RV ACCOUNT, not a home account... The reason...
Many get a home account and take a receiver with them in the RV, exactly as you plan to do, Drive a few hundred miles and suddenly the latest episode of SURVIVOR on network TV is not there.. In fact none of the big networks (ABC NBC, CBS and so on) are there. The reason is your Local Network television stations are "Spot beamed" and you drove out of the spot (Think of a spot light you drove out of the light and into the dark, it is not like a spot beam, it is a spot beam).
With an RV account, you qualify for "Distant Network Service" with DirecTV you get your choice of the NYC area or Los Angles area. network stations (or both)
And you can still carry the spare receiver into the house and use it there.