Hey there, welcome aboard. Love the filing cabinet design. Starting to see a few members here making them. I have an idea for you on your issue with the smoke leaking out. Take some aluminum foil, however long of an edge you need to seal up and fold it in half a few times till its about 1-2 inches wide, then fold that over the edge of the cabinet where you want to seal. When the cabinet drawer is closed, it will mash the foil and make a fairly tight seal. You might have to use some high temp gasket seal to make the foil adhere and not fall off, but it does work. I use it on my reverse flow lid and it works like a champ. No leaks. As far as insulating your unit, there are several options, all depending on how much to want to invest in it and or looks. You could get some KILN insulation of ebay. 1" thick will be good go for 1500 plus degrees and it insulates great. Basically make a wrap around the cabinet sides and top. You could even do build a small wood box around it along with the insulation, make it look like an old outhouse or something. Just and idea. You would then have a well insulated smoker and decorative exterior, so to speak. Keep us updated with photos and your smokes. Great job.