Amazon.com: Ezy Storage IP67 Rated 50 Liter Waterproof Plastic Storage Tote with Airtight Lid for Kitchen, Bedroom, Garage, Shed, and Bathroom Storage, Clear : Health & Household
Ezy Storage Water-Proof IP67 - YouTube
Probably the most space efficient airtight (waterproof) box for 12 spools and some desiccant - "Ezy Storage 32L/33.8qt Waterproof tote". Only about 1/8" space on top remains once lid is closed :