I made two cylinder molds using PVC pipe. While in the store, I found they had caps that fit on the pipe and I bought them. When I make the soap, I can cap the bottom (obviously), but when the tube is filled (one inch from the top), can I cap the top and leave it upright or should I close it by rubber banding it with a wrapping of paper and saran wrap? I'm wondering if the airtight container will affect the heat level of the soap making too hot. Thanks for your help.