Hello all from Mansfield TX. First post but Ive been lingering for some time. Another Newb with yet another RF build I know all the reverse flow horizontal build must get old to the pros here, but us newbs have to start somewhere. I just like the project and working with metal, and Ive been itching to build something new... A neighbor gave me a 14 x 30 air tank that I thought would be a perfect smoker project. Then I sourced a a 12 gal air tank locally for 20.00. All other costs so far has just been cut off wheels and welding wire. I was told the tank was a 30 gallon, so the 12 gallon in my mind originally was perfect. It wasnt until I measured that the tank ended up being a 14x30 or 20 gallon...Heck, looking at it I knew the tank was way to large. Plans are a small efficient RF backyard rib smoker. CC is 14x30, firebox (currently) is 12x25. CC to fire box football opening is a 6.25" diameter. Feldon say my fire box is 186% or 86% too large and my opening needs to be 7.59" I need some advice. I'm in the beginning stages of my build so I'm not so far off I cant shorten it .According to the calculation I have to make it smaller. With my tools it will be a chore with cutoff wheels to cut 2 perfect circles to make the firebox something more manageable like a 12x15. The plan is to use the end of the firebox as the door to make it easy to scrape out the ashes. Another option is to raise the floor of the firebox, which I'm a bit against because I like the space for larger chunks or small logs. What are your thoughts...do I have no option other than shortening the firebox, can this large of size work?