Since you have cable and plan to keep it I will assume that your RV travels are just from time to time and not long term making it necessary to pay for cable and satellite TV. If that's the case and your camping is not way out in the boonies then the best option for you might simply to watch TV using your free OTA TV antenna. You should get all the major Networks plus some sub channels in SD which might accommodate most of your needs. You could also bring along some DVD's for those times when "there's nothing on TV".
If you want to go satellite TV then I recommend Dish Network as they have a Pay-as-you-go plan where you just pay in advance for a month at a time and at the end of the month the service simply stops. You will need to buy a receiver and a satellite TV antenna (automatic dome or an inexpensive open face antenna that you must point yourself). You will be out $300-$600 for the setup but after than the ongoing cost should be around $50/month for the TV service. Higher cost service is available depending upon the programming you like.