Google "scuba box" 44ltr and 50ltr are ideal.... the 44ltr version holds 6 full reels of filament and a dozen "samples" of 5 or 10mtr
the boxes are watertight and airtight as well as being black to stop UV degradation
I use the 44ltr size with 500grams (a pound weight) coloured silica gel (google) which changes colour when it gets damp... then dry it for a few minutes in a microwave.
should be easy for you.... I'm in the uk and had to find an importer for the scuba box... thanks solent plastics (for anyone in the uk or eu.