We were in a similar situation when we still owned our house. We elected to keep the cable for signal quality (e.g. no rain fade) and for internet service. In addition we knew we would be selling our home in a couple years so it didn't seem to make much sense. We purchased a 211z and a Tailgater to use with the RV.
The only issue with that was with the RV plan we had to pay for a full month for every month we wanted to use it. Living in AZ we would normally take our RV out once a month and usually just for a 3 night weekend. So in affect we were paying $30+ a day for satellite for the 3 days used (our plan is $97.02 a month, including HD). Some will claim you can use it for 3 days and have it discontinued to receive a refund. However that is not Dish's policy.
Now that we fulltime we continue to use Dish and the lack of DNS isn't an issue. As we travel throughout the US we just keep changing our service address to receive the main networks (i.e. NBC, CBS, ABC, etc.).