My Gateway 30 Gallon Hanging Rack arrived today and if fits perfectly on my WSM "Classic" 18.5". I plan to cook-up some meat via the Hanging Rack System within the next few weeks.
With that coverd, I'd at least use a water pan as a heat deflector. Without it, you'd have some serious direct heat on the lower ends of those ribs.
Well, sort of....
You do realize that most people hanging ribs for competition on drums are going for color and then wrapping and laying on the cook grate? Often times with a deflector in place-as is the case with Gateways since the ribs hang and cook direct. just sayin'.
Make sure your bullet is tight and regulate the intake with 1 vent. 275-300*. You should get a feel to how long the ribs are on the hooks so, they don't lay in the basket, trim if you have to or cut in half.
As far as placing the temp probe, I'd suggest placing it on the rack. This was on my 22" using a Hunsaker Vortex basket.
My WSM's were drafty and road weary from comps and when I hung stuff on them that required tight temp control I used the GURU, stuff like chicken or tri-tips I didn't care about the runaway temps.
The drums are a lot tighter and cook moister IMO. I hang a lot and have a Gateway and Hunsaker clones and cook with both style baskets (open direct and the HSSV).
I have a 30 gallon drum, but never hung stuff on the 18" WSM.