Caution to those who place a square of paper towel inside of your tin: it will work, but it will cause rust in no time at all. Do it 3-4 times in the same tin and you'll probably start to see rust form... It does work fine in a pinch, though.
For that reason, I personally ring 2-3 days worth of tobacco around the edges of a Glad container and place a damp square of paper towel in the middle. I then reseal the container and place it in a freezer bag. Within a couple hours, you should have moist tobacco so open it up, check, and throw out the square if it has moistened to your tastes... This should stay good for several days; after that, the flavour starts to leave the rehydrated tobacco IMO. You also don't want to risk mold.
That is why I would personally avoid the "bowl" method because I prefer to rehydrate small quantities at a time. I think something is lost when you rehydrate tobacco, and even more is lost when you do it on a large scale...
An ounce of prevention is worth a pound of cure, though, so if at all possible don't let your tobacco dry out.
To Jim/twangthang above, EVERY Dan tobacco tin I've ever seen comes bone dry. I will be avoiding their products like the plague as a result... I don't think it does their blends any favours. I guess its a moot point since 90% of Dan tins are out of stock all the time.