FWIW, I have the BTLE and had to play with it to get satisfactory results. Like everyone else, when I assembled it I calked all places that were recommended. I then made tuning plates from 3/16 steel and also a baffle plate that I made 14-1/2" and I used an angle grinder to shape the baffle plate to fit the cc side of the FB at a 45*angle. I used high temp sealer on the FB door and the seam between the fb and cc. I then use a red ATV that was rated for temps up to 700* if I recall. I eventually put some fire place door gasket around the cc door. the bottom of the door gasket came loose and I haven't replaced it as yet but the doors should have adequate seals. I had no real complaints about the the temps other than I had to really stoke the thing to get the temps to where I wanted them! Then it was a battle to maintain but it was much better than my little char broil smoker. I ended up removing the tuning plates because I had too much heat at the chimney end and couldn't get temps even across the grates. I even removed the baffle plate for a couple of smokes and still have more heat the exhaust end of the cc. I put in the ceramic lava rock and did a couple of smokes and then added the baffle plate back in and I started to gain some ground. So for the initial start up I use royal oak briquettes with the hickory pieces in it and get my smoker to temps I want and add my wood of choice such as apple ,cherry etc. I add my choice of wood for a period that I determine I will wrap in foil, such as ribs the 3-2-1 method or poultry up to a temp of 140* and maybe a little more. I will add maybe half a chimney of charcoal and will add a larger chunk of wood to keep the heat that I can regulate with the vent on the FB. Since I have lost the gasket on the bottom of my cc door, I find no difference when it was on as to when it came off where regulating is concerned.
I see smoke seeping out around the door with fresh wood or re-fueling but it subsides and goes directly to the chimney once it is burning. It seems that the smoke is more dense than the heat its self, I have not worried about smoke leakage as much as keeping the temps, keeping in mind that where smoke escapes I believe the heat is going also. Once I get that thin blue smoke. I start to have more stable even temps. So my advice is to keep sealing where you think it leaking smoke excessively and get those sealed and then work on the tuning plates but keep the charcoal basket thru al your trials, it is a must in my opinion. Like everyone else, I did the mods to my specific smoker that others have done to the same model with different results. I think I went backwards by not trying a smoke without all the out of the box mods that some have done. In my case I think the mods I did that mirrored the other BTLE users should have been done after a trial smoke or 2, I'm back down to nearly out of the box setup but still tweaking, Heck I'm a guy, I have to tweak to the point of having to go back and start again! I feel your pain about not being able to keep temps but charcoal smokers are not set and forget smokers. Your oven or electric will do that for you. Keep tweaking for best results for your smoker, Our forefathers didn't have all the thermometers and gadgets we have today to smoke. Good luck!