That will work, I would just look for something better than the 55 Gallon drums. They are really thin and will not help with temp control. The build that I did is pretty similar to what you are doing. What I have noticed is the vertical box will climb in temps faster than the horizontal section when firing it up due to the fire being directly below. After the smoker is up to temp the smoker stabilized really nice, the biggest temp difference is actually the top and bottom shelf in the horizontal section. My temp readings doing a dry run with 3 maverick probes are as follow. The horizontal bottom shelf 225, top shelf 245-250, the vertical cabinet 227. I did a full cook out this weekend with an 11# brisket (13hrs), 3 shoulders (15hrs), and 3 whole chickens (4 1/2 hrs) cut in half in the vertical and I had 8 racks of St.louis ribs (5 1/2 hrs) in the vertical and everything was great. Let me know if you have any questions and I will try to help.