I bought a used cooker and a trailer to build it on to and I have a few questions that I cant seem to find the answers to. here is what I'm starting with. It was set up as a grill so it needs some modification to make it a reverse flow type cooker. I've had a vision in my head for years for a reverse flow with the firebox centered. I'm going to weld the 2 doors together so I can easily get rid of the gap between the doors. ill use the existing smoke stacks for the counter weights on the door. I need to cut the bottom of the tank out because of rot. I have a couple things I need some clarification on. I don't know how many gallons this tank was initially and I am terrible with math. The tank is 67" tip to tip inside and 52.5" to the center of the welds and 36" inside diameter, so I don't know how to enter it into the calculator to get the proper volume. Originally I planned to make a plate steel fire box but my wife doesn't work and I have 4 kids so money savings is what I'm after. I work in the trailer business so I'm trying to use scrap I can get for next to nothing. plate steel isn't something I can get easily. I went on a gathering spree the other day and I got 60' of 1" angle for the grill frames and slides and I got 3 pieces of 2x8 tube steel 6' long. I also got another tank to cut into a firebox from a scrap yard. here is my idea that im hoping you guys can help me with. I've read that too big of a firebox is easier to work with than too small and since I couldn't figure out the correct volume of my CC I put in the total length of 67" into the calculator. the tank I got for the FB is also 36" diameter. I want to cut 24" out of it so the FB would be 24"x36".. here's where I'm needing advice. because the bottom of the CC is rotted I took the 2x8s and cut them to 52.5" and cut out the bottom from the welds and cut out 8" from the bottom which will leave me plenty of thickness to weld to. I am hoping to take 2 of the 2x8s and cut one side out of each and weld them together into one 4x8 to weld into the bottom and use that as my reverse flow plate. each end will be open so I am hoping this will be big enough to allow proper flow. what im not sure of is how big the opening between the firebox to the cook chamber will need to be. I would like to use what I have on hand and run a short piece of 4x8 from the FB to the bottom of the CC 4x8. do you guys think that'll be enough. I am going to turn the CC on the rear of the trailer and have the FB between the tires. I am planning to find a 6" pipe to use for the exhaust centered at the top of the CC. I plan to have 2 racks in the CC. this will be my build thread so any help is greatly appreciated.