As Ak Nimrod has already said, the weather can be rather nasty in September, even in SE. Generally, early in September, the weather can be fairly pleasant, but then again, I've seen it blow up the worst storms of the year. As for as the scenery in SE, it can be grand, and then again I've seen it where you couldn't see much over 500 ft above sea level for days or even weeks. In September you will find black bear anywhere from the streams and tide flats to the top of the mountains. I would agree with Ak Nimrod, that a spring hunt would be much better, even in SE. As the bear are more likely to be found on the beaches, tide flats, open creek bottoms and open ridges. I would be looking somewhere between mid-May to mid-June, but that depends upon the winter snow depth and how warm the spring may be. Most of the larger Islands in SE support a black bear population of some sort, except Admiralty Island, only brownies there. Even the main land has a good black bear population, if you know where to look. As for the do's and don't... "do" bring along rain gear and "don't" forget your rain gear. There are bear guides in most of the communitities from Haines/Skagway to Ketchikan. Check with any air charter services for good reliable bear information. I have included a link for F&G area Biologists. Just remember that they are some times new to an area, some will not be completely honest with you, and some will try to discourage you from hunting in thier area all together.
Fish and Game Wildlife Biologist
Hope this info has been helpfull.