Choosing and buying a used or new RV and modifying it for special use is a complex matter. Recommend you get (and take advice) from established rescue groups before making plans for rescue transporting and making contacts in other states to find dogs homes. Also, get advice on using/modifying an RV or other vehicle from rescue groups as well as interstate regulations. Single-handed transporting, camping, and exercising a number of dogs in hot or stormy weather may not be practical/doable. Admire your wanting to do this!!!