Check out this guide from bbqinstitute.com:
Additionally, I would recommend the following:
- Build a 5 sided charcoal box out of expanded metal to fit into your firebox. Raw metal, not painted or treated. This keeps coal and wood together in a tighter area and also allows you to stack up your wood/charcoal.
- Get a digital thermo that has two probes, one for meat, and one for the cooking chamber.
- Invstigate "tuning plates" for the bottom of the cooking chamber - search this forum and you'll find out what these puppies are - they help to distribute heat. This will also involve some new bolts to support a higher grate position for the lower grate.
- Seal up the cooking chamber door for when it's closed, there are several methods. I used a hi-temp food grade silicone and greased the lid with Crisco so only the bottom of the silicone adhered and the top cured without adhering to the lid.