Gregg's dead on the money! No need to foil, spritz, or mess with your ribs during the smoke. "No peeky" is the way to go! Ribs are a timed cook, which can vary up to an hour. It's a feel thing, that you'll learn after a smoke or two.
Start checking them around 5 hours. If they look done (good bark, and some surface moisture), and the toothpick goes in easy, and you can pull the meat sideways without it breaking, you are good to go! If not, give them another 20-30 minutes and check again.
I'm not sure if you've ever smoked ribs before in any other smoker, so I want to remind you to remove the silver skin (the membrane on the bone-side of the ribs). If you don't, you won't get any rub/smoke penetration on that side, and it's really tough when cooked. Start with a butter knife in the middle of the rack, and work it under the membrane from one side of the rack to the other side. You create a "pocket" under the membrane. Grab the pocket like a handle, and pull up. The membrane will remove from the middle out, nice and clean! Once you get this technique down, you'll skin 3 racks in about 2 minutes!
Check out the pork section for recipes - lots of good ones for ribs there!