Jackie, baby backs are a great first smoke! 3 racks won't fit on one shelf in the #2. I usually always do 3 racks at a time, and I cut them in 1/2 racks, placing them on 3 shelves. I put the thick ends on the lowest shelf, and the thinnest on the top. You can guess what goes on the middle shelf.
When you unwrap your ribs from Sam's, remove the silver skin on the bone side (the tough membrane). A butter knife, starting in the middle of the rack, works great. Make a pocket and then lift up on the skin like a handle - the skin will pull right off to each end. This takes a little practice, but it's important. Halve the racks so you have 6 half racks.
Then, coat the ribs with yellow mustard and your rub of choice. Wrap the ribs in plastic, and let them get happy in the fridge overnight.
Place a pan (I use disposable aluminum "mini loaf" pans) of apple juice on the bottom of the smoker, next to the smoke box. Of course, this is after you foil the bottom and the top of the smoke box - don't forget to poke a hole in the foil for the drain/air hole in the bottom!
Put the ribs in, and dial up to 235. Now, you want as little "human intervention" as possible! Don't peek until at least 5 hours. At that point, open the door and check out your ribs. I use a wooden toothpick to test for doneness. Stick it in the meat, next to the bone. If it's tender, you're getting there. Then, pull sideways to see if the meat will easily separate from the bone. If it doesn't, or the toothpick breaks, close the door and give it another 20 minutes and test again. The timing is not exact on ribs - it's a "feel" thing. When they're nice and tender, and pulling away from the bone, they're done!
At 235, 3 racks will take me 5- 5 3/4 hours. You just have to check them. When they're done, you really don't have to "rest" ribs, but they slice easier if you let them sit on the cutting board for 10-15 minutes. No need to foil with apple juice; they'll be plenty tender and moist!
Welcome to the "Lazy Q, No Peeky" method of ribs!! ;D
All kidding aside - just put it on the same level, but not too close. 
