I use the same exact smoker for my traveling smoker, when I drag my travel trailer around the nation, and yes, it does let some smoke escape. BUT, remember, the operative guidelines on this site is THIN BLUE SMOKE. If you've got a lot of smoke escaping, you've probably got too much being generated anyway and the leaks are helping you. OK, that is a kinda tongue in cheek response, but it's not far from the truth. I use to be in that crowd that thought lots of smoke was good (before SMF days, then I became enlightened) but now understand that was not the right attitude to take.
There are several threads, as mentioned above, for sealing your doors and such.....Believe me, I've made some mods to my Big Block GOSM that would make you wonder if it was a BBGOSM or a MES (glass door). Yes the glass door is neat but halfway through the smoke, the glass gets difficult to see through and you really need a BRIGHT flashlight to peek in. I guess what I'm wandering around to is: Is the smoke really a problem? Are you losing a lot of heat or is it slow to get to temps? If it's just smoke, then back off on the smoke generation. If it's hard to get the temps up to the desired temp, then your question about sealing is more for heat containment. I really don't have a problem getting the temp up to the 225 to 250 range (ok, if I'm not watching it carefully, 275) so it's ok for me. Come winter time is going to be the real challenge. Yes, I try to smoke 365 days a year, if I can, but then where I live is fairly moderate in the temps (just tons of rain). So if heat containment is your real problem, seal it up. Oven gaskets seem to be the best option. The glues to keep it in place has always bothered me. Several members have resolved that problem. By The Way: just because this smoker is small doesn't mean you can't crank out some great smokes from it. It might not be the biggest on the block, but I'll tell you what, I'm still figuring on doing a 14 lb turkey in it. You betcha. Creativity is the rule. Now, go forth and smoke something.