New here, looking for some advise. I'm about to build a reverse flow smoker from a 120 gallon propane tank and need some advise on sizing the fire box. I have watched several builds and they seem to have large fireboxes but only build small fires in them. My cooking chamber is about 5' long and 2' in diameter. I'm planning on using a 4" pipe for the exhaust. Any advise would be appreciated.