The solar drier got no use after February since no more filament got wet & no more filament came from a factory in a hydrated state.  This created a real need to use the container for long term storage as well as solar drying.  It's not as air tight as the long term storage but it could be air tight enough. 

The ideal solution would be completely wireless to avoid puncturing the container.  There would be a self contained board with radio, sensor, fan controller.  This would be inductively powered from the outside.   An off the shelf charger might do the job.  The boards would stick together with magnets.  The fan would run continuously while the sensor & radio would just provide monitoring.

The mane problem is the container has to be vertical for solar drying & horizontal for long term storage. 

The home made desiccant bags failed while leading candidates have moved to acrylic cups which have to be upright.  There has to be a way to monitor the desiccant & it has to be in a waterproof container because it liquefies suddenly.  A paper towel lid might be good enough to transport it, but it can't be stored sideways.  Some PETG lids could be tested to find the maximum hole size.

It almost needs different desiccant containers for horizontal storage & vertical drying.  The only room for desiccant & place where it won't fall over is the filament hole.  The only acrylic in the right size might be pipe stock.  It would need a waterproof end cap.  Even then, the hole isn't always going to be right side up.