I made a cereal storage box based filament drybox with the smaller RS1 membrane from Rosahl. Works pretty well for keeping new (fresh unpacked) spools or pre-dried spools (lying around for days/weeks before) at 15% rel. humidity (compared to 60% outside in my region). And consumes just 0.2W power at that level constantly. Made a bunch of 3D printed parts for it and it’s powered from USB. See on Printable.com if interested: Printables
I also grabbed a larger M-3M1R membrane which currently keeps a 50l storage box with 15 spools at constantly 15% rel. humidity. Also made a 3D printed mounting cover with USB supply but that’s not yet on Printables. Will add soon.
Yes, these membranes are a bit costly but they are very, very efficient in the long term compared to regularly using some Sunlu filament dryer or even an oven to dry spools or recover desiccant. I use four of the RS1 based dryboxes with the filament types I use frequently which is still less than 1W of constant power.
Cheers,
ER!K