You need to use water and also a foiled pan just so you will know how water affects the temp. I cooked baby backs last Sat. at 280 and used water. I like water with ribs. I think it helps keep them from drying out. Water will cause you to go through more charcoal as you have to keep the water at the cooking temp or higher but I think it is worth it. My reasoning is that many of the other really good vertical smokers use a water pan. Backwoods comes to mind.
If I don't use water, I have a clay flower pot base I put in the pan and then cover both with foil. If you use water, spray the pan with Pam before adding water. Makes clean up a breeze.
Smooth Smoke BBQ Team, KCBS CBJ, 2-WSM, Cajun Bandit Conversion, wsm 2880, Smokey Joe Mini wsm, Old Country offset, several kettles.