One way is a mixture of sea sand and iodine crystals in the bottom of a wide mouth jar with a lid. The lid keep the iodine vapor in place. I also just put a small 1 g bottle of iodine in a wide-mouth jar with a lid. The chamber is set up a few hours before you need it to allow the iodine to sublime. When you use it, dry the solvent from the TLC plate, place it in the jar, and then screw the lid on. when done, Remove the plate, replace the lid, and image the plate.