Eric - I did put foil over the top of the pan after I added the water. I'm not sure how the steam escapes, but I do it because it makes clean-up way easier. Instead of ending up with all the dripping fat mixed in with the water, it collects on the top of the foil, and all I have to do is crumple the foil up and pitch it in the trash can.
And yes, I went low and slow. My temperature generally fluctuated somewhere between 225 and 250 all day, which is right where I like it.
As for the kitchen twine, I don't know if it really helps or not, it's just one of those things I've always done when cooking a butt. It doesn't hurt, so I've never stopped doing it.
Thanks for the comments guys!