Are you getting a lot of leaks around the door? A little bit of leakage shouldn't be a problem. If the leaks are significant, I would try to shape the door to get a better seal and ensure the latch is doing it's job correctly.  I've put the Cajun Bandit SS doors on both my WSM as I just didn't like the thin flimsy door. I get just a  tiny bit of smoke leaking but nothing that I am concerned about and my temps are usually pretty good  - except for one cook a couple of years ago where the door/latch issue was gaping and yea, temps shot up. So a significant bad seal can play havoc. 
If you want the thing as tight as possible then I would think a properly installed gasekt would do the trick. I'm just wondering that with a properly fitting door how much it effects the cook.  
I agree with Bob Ivey that there seems to be some  latley that had some temps issues, but I'm not so sure if it's an air control issue or more of  a heat sink issue.  The few threads I've read  I've noticed the heat issues were with set ups that were trying  to dial in a process without water in the pan, or with the pan touching the charcaol, IMHO.