For a period of only one month I can't see purchasing any RV. A rental should be ready to go and you may have all kinds of little things to deal with on a used unit. If you are interested in seeing any cities it is difficult without a vehicle to drive. New York City is one exception with a CG across the river in New Jersey. I would also recommend beginning your trip 4-6 weeks later, in the Southern part of the US and go North to Canada for the end of the trip. The Maritime provinces have some great scenery.