Priority and Ground Advantage are two entirely different classes of shipments. You pick one or the other. You can use the free USPS Priority boxes for Priority but you CAN NOT use them for Ground Advantage.
"Laissez-faire capitalism (AKA The Great Material Continuum) is the only social system based on the recognition of individual rights and, therefore, the only system that bans force from social relationships." ~ Ayn Rand
