Carl, it is pretty simple when going from your old S&B to an RV full time. Your billing address and service address will change. However, your billing and service address do not have to be the same.
You can take your current receivers with you, but you will need a dish. You can have a dome (no HD), or you can spend the money and have a Wineguard automatic dish installed on top of your RV (HD). Direct-TV does not install these systems but any RV dealer that sells them will.
We went with the automatic dish because I didn't want to be one of the guys standing out on my site for 20 minutes trying to aim a dish to get a signal several times a week. Also, after being on the road for awhile we found out that we didn't need to constantly change our service address and get local channels with Direct-TV. It was easier to just use our RV antenna to get the local channels and then use Direct-TV for all the other channels.