I'm nearing the end of my build of two 55 gal drums welded together end to end and one 55 gal drum on the bottom as the firebox. I have two 6" holes coming from the bottom of the firebox with flues leading into the cook chamber. I am going to have a plate the runs all the way across the bottom of the cooking chamber with gaps on both ends. I have tried using a calculator to figure out the gap I should leave on both ends to make flow correct but since this is an oddball build it won't work. The plate is 18 1/2 wide which leaves roughly 4 1/2 to 5 inches under it to the bottom of the cook chamber. Any ideas on how much of a gap I should use on both ends, or should I just guess 5 inches on both sides and add plates to fill some of the gaps on both ends later if it flows slow or too fast?