Your best bet will be to purchase the RV in Canada or the USA and drive it down and obtain the importation permit at the border.
Why do I say that for the simple reason that trying to legalise the transfer of a foreign registered vehicle will be time and money consuming, poaperwork has to be translated and notarized, and not everyone can translate the paperwork, it has to be an aproved translator, or done by the US or Canadian Embassy or Consulat.
After that you need to obtain a new temporary importation permit and not every little town has the proper place to do that so havoid headaches and purchase the vehicle abroad and get TIP at the border it will be faster and cheaper.
navegator
