I store all my filament in a big Ikea Samla box with an added gasket/weather strip for the lid and 1kg of desiccant pearls. According to the cheap hygrometer on the lid the RH in there stays at around 20% while the RH in my room is typically somewhere in the 30s.
Really low RH values are hard to reach without something like an active heater that drives moisture out, and you most likely also need a "better" hygrometer to even monitor that since the cheap ones AFAIK can't even measure low values properly.