Dish offers a special service for RV users that you can get national network
channels (ABC, CBS, NBC out of NY or LA) for an extra $5 per month and
providing them a form that you can download from their website and a copy of
your registration. I think DirectTV has a similar program, but has more
restrictions. I think Jim is right that you cannot get the local channels
from a particular city outside a certain limited range.
Jarrod