There is a rescue in TX that rescues dogs from the border shelters and transports them after they are pre-adopted to various cities in the US . They have a heavy duty utility trailer( long one) and can transport somewhere between 50-75 dogs each trip. The kennels inside are double stacked and it's air conditioned. They have outdoor temp kennels that they unload the dogs into and stop for potty breaks. Each kennel has water and a blanket, toy etc. Very small dogs or puppies may be doubled up or maybe 4 to a larger kennel. It can be done, but an rv probably isnt the best choice. This rescue is TracyDogs out of San Antonio - soon moving to a new facility, I think in Hondo Tx. You could try contacting them for ideas.