<p>The multi-degree-of-freedom (DOF) vibrations experienced by mobile robots on outdoor terrain can degrade payload stability. This paper proposes a dual-stage, underactuated vibration isolator (VI) for mitigating these payload vibrations. The proposed VI can attenuate vibrations in five-directional motions using three actuators. The dynamic analysis verifies that the proposed mechanical design partitions the coupled multi-DOF dynamics into three largely decoupled groups: heave, pitch, and roll. This inherent decoupling enables a simplified and partitioned control strategy. A disturbance observer (DOB)-based controller ensures robust attitude stabilization for pitch and roll, while a skyhook controller actively suppresses heave motion. This paper validates the proposed VI experimentally on a mobile robot under realistic operating conditions. A comprehensive set of trials, including tests with a vibration-sensitive liquid payload, demonstrates robust multi-DOF vibration suppression and attitude stabilization. The proposed VI effectively ensures the stability and integrity of payloads in challenging outdoor environments.</p>