The current-generation RTGs (both GPHS and MOD) are designed for operation in a vacuum environment.The raultifoil thermal insulation used in those RTGs only functions well in a good vacuum.Current RTGs are designed to operate with an inert cover gas before launch, and to be vented to space vacuum after launch. Both RTGs are sealed with a large number of metallic Crings.Those seals are adequate for retaining the inert-gas overpressure during short-term launch operations, but would not be adequate to prevent intrusion of the Martian atmospheric gases during long-term operations there. Therefore, for the Mars Rover application, those RTGs must be modified to prevent the buildup of significant pressures of Mars atmosphere or of helium (from alpha decay of the fuel).In addition, a Mars Rover RTG needs to withstand a long-term dynamic environment that is much more severe than that seen by an RTG on an orbiting spacecraft or on a stationary planetary lander. This paper describes a typical Rover mission, its requirements, the environment it imposes on the RTG, and a design approach for making the RTG operable in such an environment. Specific RTG designs for various thermoelectric element alternatives are presented.