There are good discussions about this on IRV2 and on the Escapees boards. Here's a quote from someone with much more experience than me:
Tis a very murky area at the moment. FCC doesn't seem to care, but Starband, and others, have "claimed" they do as rationale for not supporting installations that are mobile. I was a Starband subscriber for a year, and a certified installer. If you move outside the footprint of your transmit delay parameters you must get assistance from their technical support folks to reset them (aiming the dish and getting a good signal was never a problem for me - getting parameters reset could take from 30 minutes to 3 days!). I was never challenged the few times I moved. SOME WERE! Some folks had their service disconnected when Starband discovered they were in an RV . Their $600 investment became useless . I think you could get by with a twice-a-year snowbird situation, but be prepared for an expensive and not very satisfying internet experience. I have no experience with the Direct system. They are waiting on approval to merge. As I said, Tis murky!