I use Ezy Storage 18L waterproof boxes as filament storage. Each box can hold 4 BBL rolls and they're light weight. The boxes have a seal so I've made a bracket to hold a round hygrometer / thermometer which attaches to the lid using 2 x 5mm M3 screws. There's a template for drilling the holes, you line the notch up with the center rib on the lid.