Check Stonewall on RoG for a good overview of S3 junglers:
Like Wylwist said, focus on those with good sustain. Assuming your Seals are Armor, that will help. For Masteries, I would actually put 2 points in Butcher, and possibly others in the Offense tree depending on your champion. The key Defensive masteries are the ones that increase health and reduce physical damage, plus Bladed Armor - so you don't really need 21 points there.
Now, go play around against bots to find a couple of jungle routes that work for you, recognizinig that what is ideal for a 30 with Tier 3 and a hard leash is probably not the best for a 20 with Tier 2 and no leash. (You may get a leash at 20, but don't count on it.) You need to figure out when you can realistically gank (i.e. you have buff(s) but are not too low on health) and when you should base. It can take a bit to work this out for yourself, because you can't just steal something from a guide in most cases.
But it's definitely doable.