I am thinking of using one of these humidity controllers to automatically turn the fan on/off and keep the humidity inside the box at 50% (or whatever ideal drying/curing RH is). Have another fan inside to circulate the air around the buds. I haven't figured out how to have the fan always going at a very slow rate to keep negative pressure but then go up higher when the controller kicks in. Maybe stack two fans?
get a small one cut out for it and tape her in