My typical process for spares is to butcher them into a St. Louis cut, remove the silver skin and excess fat, and coat with a layer of yellow mustard and a heavy application of my rub, wrap in plastic and refrigerate overnight.
They go in the smoker at 225 with 3-4 oz. of applewood or hickory. And that's it for 4.5 hours. No peeking ... no foiling ... no spritzing. After 4.5 hours, I typically coat with a layer of sauce and let smoke for 60 to 90 minutes until I see the pull back on the bones that I like.
I've never had a problem with moistness; if you're concerned, a couple of hours in apple juice before you rub them and wrap them overnight would more than boost it for you.