Não consegui encontrar uma página oficial que abordasse o peso do veículo e das licenças estrangeiras, por isso dirijo-me aos camionistas que alugam agências e encontrei a resposta.
With a normal driving licence you are allowed to drive every recreational vehicle. It doesn't matter if it's a small motorhome or a large buscamper. The U.S. has an agreement with most countries whereby the renter's full national driving license may be used for a period of up to one year in the U.S.A. International Driving Permits are generally not required in the U.S.A but it is recommended to carry one. If they are taken, they are only valid in conjunction with a full national driving license.
e de moturis.com :
DRIVER’S REQUIREMENTS
Drivers License A national automobile driver's license is required. We recommend customers to carry a translation of the national driver's license or an international driver's license, but under any circumstances, customer must provide a valid national driver's license at pick-up.
Drivers Age Minimum age is 21 years for all vehicles
A partir disso, entendo que qualquer licença de motorista é bem-vinda, contanto que você tenha 21 anos e a licença seja em inglês ou que você tenha uma licença internacional junto com ela.