I doubt the seal is your problem. How many boxes are in your cooler? Are you using empty boxes to fill the excess space? Are you re-hydrating your beads because most have turned white or only because more than 1/3 are white? What kind of hygrometer are you using and where is it placed? Try putting the hygrometer inside one of the boxes for 24 hours and then get a reading.
A less than full cooler will force the beads to rehydrate the remaining air each time you open it up. In a dry climate like AZ this could mean bringing all the extra air from the low teens back up to 65% each time you open.
