You do understand that your dome will never be able to receive ANY of the DirecTV HD programming. If you are OK with SD only in the RV then there are a couple of other caveats. The receiver cannot be an H25, Genie (HR34, 44, 54) or a client used with a Genie. My suggestion would be the H24 (or get a D12 since you will be SD only an leave it in the RV). The other setting that might work with your old dome is the Oval 3 LNB. Just be sure that you get the multiswitch setting off SWM and changed to Multiswitch. The antenna options are numbered and 18" round is #1 and I believe the Oval setting is #3.