Miss. Code Ann. § 75-57-37

All containers and pertinent equipment owned or in use by the government of the United States of America are exempt from the provisions of this chapter. Liquefied petroleum gas containers using liquefied petroleum gas as a fuel to propel recreational vehicles, automobiles, trucks and other vehicles, or used as a source of fuel to produce light, heat, power, refrigeration of air conditioning on mobile homes, recreational vehicles, campers, etc., that are in interstate travel, and designed, fabricated, tested and marked in accordance with the regulations of the United States Department of Transportation (DOT) or the United States Interstate Commerce Commission (ICC) and all cylinders with a water capacity of less than two hundred fifty (250) pounds, when used for other than motor fuel purposes in this state, are exempt from inspection.