I have used a trick suggested to me by an old pipe smoker long gone (Bless him) and it works very well indeed.
Take a carrot and cut a portion off. It doesn't need to be big at all, say about the size of a penny and about 3 times as thick. Place the piece of carrot in to your jar or pouch and leave there for a couple of days. You can check it each day and turn the tobacco over with your fingers to ensure it doesn't get too wet in just one place and gains a standard level of moisture all over.
As I have said, I use this method myself and it is very effective. It greatly reduces the chance of the tobacco getting too wet, and the best bit is that it is a very very cheap way of doing it.
Any vegetable could be used, but I would stay away from those that have a strong taste or smell to them. Potato, Swede, Cabbage stems are also good.
"A pipe gives a wise man time to think and a fool something to stick in his mouth." - C.S. Lewis