You didn't mention which sat service or if HD is required. You said portable but didn't state manual or automated satellite acquisition. For Directv HD there are no capable portables domes, for Dish HD it can be done but most can only feed 2 receivers and they must be on the same satellite.
No doubt the best choice is the Winegard Traveler mounted on your rig's roof which would solve almost any want or desire for sat service in your RV. On a new RV purchase I'm sure you could work out a deal with the selling dealer to have one installed before delivery.
We have had HD sat service in our rig since it became available. We RV on many instances where exposure to the southern sky is limited and thus have always purchased the same HD dish we have at home and mounted it to a tripod or home-made stand for use on the road.
On our next new rig we will have dealer install Winegard Traveler, but we will always bring portable HD sat and over 100' of coax for the several times of year we need to move it around the campsite to acquire all three satellites when trying to point between the trees.