Get a medium sized male dog (gender is very important) that looks fierce but has a good disposition - herding dogs like the all black Belgian sheepdogs are a very good choice. This size dog will intimidate most folks and be able to leap into the motorhome and otherwise take care of itself. A male dog will consider himself to be the alpha dog and you his property which he will instinctively want to protect. The black fur really helps as well. People will be more fearful around a black Belgian or German shepherd than around a white Samoyed of the same size.
Think about all the places you have gone alone (bank, supermarket, work, hotels on business, airports, train stations, school) and realize that you were not attacked much less killed. Traveling around by RV is only different in terms of adding the possibility of breaking down on a remote little traveled section of highway. Avoid those routes or caravan those sections of road with others and you will be fine.