You can move your Hopper to your RV but you will need a standard Dish antenna like the one mounted on your house (or an automatic roof mounted unit like the Winegard Trav'ler) for it to work properly.
If you would like a separate receiver for the RV, the only receiver that Dish is currently allowing Hopper owners to add to their existing account is the 211K or 211Z (and possibly a 411 since it's the same thing with no Ethernet connection). You would then be able to leave it in the RV, only activate it when you need it, only pay the $7/month additional receiver fee and then only when it's activated.