The present invention is a loading dock rail shelter with an inflatable canopy and a dual stabilizing and passive retraction support assembly. The canopy has an outer end that moves between inflated and retracted positions. The support assembly includes a rigid frame secured around the perimeter of the canopy, and a pivoting support mechanism that allows the frame to ride with the canopy while supporting and guiding the canopy. The shelter has a lower panel assembly that close the bottom of the canopy. The lower panel has lateral support rods and a front panel support assembly secured to the frame. The support assembly supports the canopy and its lower panel so they do not drag along the ground. The rigid frame stabilizes and guides the inflating canopy to seal around a railcar doorway. The support assembly and frame swing back to passively retract and hold the canopy against the building.