I have been smoking on my Weber gas grill but want to upsize and have came across a great unit to build from. I have located a 5'x3'x3' insulated steal warming box from a restaruant quite cheap and in good condition. I plan on mounting a single propane ( fish cooker ) burner first level, rack with pan for ship, then water pan. Can someone help me with the venting I will need on this unit? Size and any design ideas would be greatly appreciated.