Unless you can get an RV waiver accepted, you would only be able to get your local package and no distants networks. As far as if the locals are availaable on the prepaid system, I do not know for sure.
You can get networks on a DishNOW receiver? That's news to me.
The two biggest problems with DishNOW is the fact that you cannot get locals and you have to pay full subscription for every receiver you want in your house. They need to make other receivers able to connect to the first one (or same dish/switch) to receive authorization for the other rooms.