Abstract: Seat belt web retractors and associated systems and methods are described herein. Web retractors assemblies configured in accordance with various embodiments of the present technology can include, for example, a frame having a first sidewall and a second sidewall opposite the first sidewall, and a spring-loaded shaft extending between the first and second sidewalls. The web retractor can further include a locking mechanism positioned proximate to the first sidewall of the frame and operably coupled to the shaft. The locking mechanism can include a vehicle inertia sensor and/or a web inertia sensor. A cover can enclose the locking mechanism such that the cover and the first sidewall form a liquid-sealed enclosure around the locking mechanism.