Based on a study of a Mobile Pressurized Laboratory (MPL) concept made during the European Mars Mission Architecture Study conducted for ESA, further design development of the laboratory and interior functional layout of the rover has been performed. This includes volume optimization, wheel system and geometry, interior layout and functional zoning, airlock placement and ergonomics, radiation protection, ergonomic detailing of habitation functions like sleep, kitchen, hygiene, ergonomics of work environment for driver, glove box, laboratory and storage systems and spatial flexibility and adaptability. The large wheel concept proposed in the ESA study to maximize habitable volume is further investigated. Additionally, omni-directional wheels have been introduced to the design to improve the vehicle's manoeuvrability. The inclusion of new design features led to a decision to rename the concept, MarsCruiserOne (MCO). The paper describes the design of the MCO.