Renting an RV is not inexpensive on my end either and the butt kicker certainly is the cost per mile. I suppose it's an effort(sounds successful to me) to get past the sharp depreciation. Local RV stores this way tend to have 1 of 2 business plans: they only rent within a certain mile radius or will tow the rv to a specific group of campgrounds also w/i their region.
This leaves longer distance rentals to the national companies who have to keep a continent wide network of mechanics and such on retainer. Not to mention their higher insurance costs.