We cook about 1500 lbs of Q (butts) to raise money for our Scout troop. Right now we have a gas cooker- about 4'x5' and a Lang 60 RF with a 120 gallon chamber. I want to build a fatboy RF to increase our capacity and shorten the cook time- right now we run about 36 hours to cook all of our butts, chop and pack. I am looking to speed things up a bit, as far a volume goes- I know we can't cook bbq in less time on the smoker and have it come out proper. I have been doing my homework, and have seen some great builds and allot of knowledge shared here. But I still have a few questions. I have a 500 gallon propane tank lined up ( about 9 ft long and over nearly 3 ft in diameter- this is an oldie but goody). Same source also has a 120 gallon vertical tank( 30" diameter x 54") to throw in. Would the 120 be big enough to make the firebox out of? is the volume there? I'm thinking it would be allot less expensive to go that route- using a smaller tank- than build a firebox out of plate. This will be a trailer rig, see trailer in pic- ignore the oval drum, it might be a chicken cooker or finisher for the butts after about 4 hours smoke on a separate trailer and gas fired, but for this build, I want to mount propane tanks for the RF and firing it with splits on this trailer. Thanks in advance for your input.