Vertical Smoker build-please critique

This is my latest project, a vertical smoker with offset firebox.
I have perused alot of different threads on various web sites and am trying to incorperate all that I have learned.

The basic dimensions are shown in the picture, and I have tweeked them some based on the BBQ Pit Builder Calculator web site.

I will be using gaskets on both the firebox and smoking chamber doors.
I plan to build it from 1/4" metal. The opening between the firebox and chamber is 12" x 6.5".

The reason for two exhaust stacks are two fold. 1) Based on the calculator, I need 6" diam. pipe, not readily available in my area, and the place I did find it, sells it in 20 foot lengths. The exhaust stacks are only 24 inches high( again, based on the calculator).
My thought process is that I can use two, 3 inch diam pipes, and by having them offset like in the picture, may create a more even air flow thru the smoking chamber.

So, if y'all dont mind, please critique my plans, both bad, and good are all welcome.
Thanks

Thanks to all the replies.
Duh, i had a drain in my mind, just forgot about it.
I also really like the idea of the deflector in the bottom, altho I may just run it about halfway accross. I can tack weld it in place and then do a couple of smokes to see how it works from there.

Again, thanks for all the input, cant wait to get started. I found a fellow with a plasma torch set up and he will cut all the 1/4" sheet metal parts for me.