First off I guess a hello is in order. My name is Shawn and I'm from Missouri. Been lurking on the forums here off and on for 3 or 4 years now but somehow have never posted. I first started smoking food over 20 years ago and have had many great successes as well as a few epic failures. I'm a guy who likes to tinker and build stuff so naturally I've dabbled with smoker builds a little bit. I've built a handful of hot and cold smokers over the years ranging from cellotex boxes to old freezers and of course mods to commercial units. I've been wanting to build a patio sized horizontal reverse flow unit for some time now and recently I found a tank that I liked so I guess it's time for a new build. I've read as much as I can but I do have some questions about fire box size. First off, the tank I'm using for the cooking chamber is 12" x 41" so it is pretty skinny in comparison to it's length. Not a big deal for me since I rarely have a need to smoke more than a couple of butts or a couple racks of ribs at the same time. I have a good idea of how I want it all to go together but my biggest concern is with having enough of a fire box without over firing it. Following the 1/3 rule would suggest that a 20lbs grill tank (12" x 14") would be the appropriate size. However, considering that this tank is so skinny, pork butts will literally come within an inch or less from the sides and top, so if this thing runs too hot it's gonna cook way too fast. I have a 13.5 lbs Primus tank that I was thinking about using, it is 9" x 13". Would really like some input from you guys who have built small and mini RF's. What are your thoughts on using a smaller fire box than the calculator recommends? Here's a pic of the tank I'm going to use. Here's a pic of the end of the tank. It is shown with the top of the tank oriented up. The mounting brackets on the back will become the base and the top of the tank will become the front. I plan to weld a couple of short extensions on those bases which the front shelf will mount to. I really want this unit to look good too but can't decide which way to orient the fire box. The following two pics show the smaller tank as the fire box and the third pic is with the 20 lbs tank for comparison. Give me your thoughts and concerns please.