Eddie's snowcat was designed by special effects assistant Mike Trim, who had been interested in snowcats since childhood. The inspiration for the design was a caterpillar-track truck concept that Trim had produced for the "Thunderbirds" episode "End of the Road". To match the construction of the puppet set, Trim was forced to alter shape of the cabin, which he felt ended up " the final model a more upright look than I had hoped for." The Frost Line domes that appear in the episode are represented not by scale models, but painted flats.