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SSR-101 'Reliable'

"After landing on another planet or moon, there's not much that can be done on foot. Thus, the Standard Science Rover series was developed, designed to give a way for Kerbals to easily explore a planet's surface, log and collect samples, and travel long distances without needing to bring spare EVA fuel. The only downside is the lack of protection for the crew, but it remains a popular choice for extended activities away from the lander."

Seats 2 kerbals. Just barely fits inside a 2.5m service bay. Made with lots of mods installed, but uses only stock parts. May be some unnecessary conflicts as a result, so just be wary.