Once you have a Hopper you will hate NOT having a Hopper. No matter what Dish might say there is no reason at all not to take the Hopper in the RV. You just need to ensure the receiver is completely powered off before traveling to ensure there is no damage to the hard drive.
The other disadvantage of using the Wally and a Pathway is that, even with the addition of a hard drive, you don't have full DVR capabilities like you would with the Hopper.
I guess some of this depends upon how long or how often you will be in the RV but I would lean toward moving the Hopper if you are going to spend a reasonable amount of time away from home.