There is no one size fits all answer to this question. However, the following steps can help you determine the best way to fit a pot to your pot smoker:
1. Measure the outside diameter of the top pot and make a template out of cardboard or paper that is the same size.
2. Drill two holes in the bottom of the top pot that are slightly smaller than the outside diameter of the top pot. Insert a U-bolt through these holes and hold in place until the glue has set.
3. Fit the bottom pot on top of the template, making sure that it fits snugly against both sides of the top pot. Glue into place with epoxy or other suitable adhesive.