Depending upon how often you will need the Dish service it might be more affordable to keep cable at home (especially if it's a bundle deal) and just pay for Dish when you are in the RV. It's a monthly service that can be cancelled and the remaining credit for that month applied to your next activation.
I recommend the Winegard Pathway X2 for the Dish pay-as-you-go service. It has the largest antenna of the portables and it can be used with both the EA and WA Dish satellites giving you much more flexibility.