I am a novice smoker but I do some plumbing and heating work. Instead of the 90's people are using for the exhausts try using tee's. Make it to where you can look through it, after installed. This will help with drafting and your windy situations. If you were to make a big cooker....they make rain caps that swivel when the wind blows.
Ohh, the longer the exhaust the harder it will want to pull and it gets worse when its cold outside.