Looks like it's coming along great! I may hold off on a final decision about your firebox location though. Having it in the middle was my original idea as well, but I was talked out of it by some other builders. I've been told that it can be very difficult to keep even heat with this set up and there is an issue with the air flow trying to move smoothly around both ends of the tank, its just not as fluid of motion as with a SFB or RF. Also, I'm no expert, and never actually tried it to see if the claims were true. I own a SFB which im considering converting to RF. With my build I ended up going vertical with the tank I had and am very happy with the results. Anyways, I would wait to see what others have to say before cutting in to the middle of the tank, but I also say theres nothing wrong with experimenting haha. I'd just hate to anyone be disappointed with a big build like this. Either way, looking great so far!