For me it doesn't get much better than Turkey cooked on a vertical roaster ala beer can Turkey style, simple seasoning and cook to perfection, a million times better than doing it in the oven not to mention the "what, you cooked this on the BBQ?" Comments.
I smoked a Turkey last year with "stuffins" (home made stuffing wrapped in bacon and shaped in a muffin tin) and it was amazingly moist tasty meat. It got be doing turkey drum sticks through the year.
I did a turkey one year. Came out fine, and you don't have to worry about the pit temp so much. The smokiness is really nice though. Just be sure take all the usual precautions with regards to safety - probe for internal temps etc. Also keep in mind that if you have people waiting for food, cooking in a smoker can be a bit unpredictable when it comes to the finish time.
re: rain - as long as the top vents are sheltered you'll be fine
I rotisserie my turkey each year on my Performer - but if you do smoke your main dish - keep the heat going and throw on some pineapple chunks dusted in cinnamon sugar and dark rum (in a foil tray) leave them on for an hour or so until beautifully soft - they're excellent with cream or ice cream