The Stannah 320 Outdoor was developed specifically for the challenging British climate — a country where rain, frost, and salt air can be expected in equal measure. Stannah's engineers created a unit that could handle the worst the weather could offer.

The 320 featured a unique "clam shell" cover design that enclosed the entire seat and controls when not in use. This provided comprehensive protection without requiring the user to remember to deploy a separate cover.

Special attention was paid to drainage — water that did enter the rail channel would be directed away from sensitive components through an integrated gutter system.