Wish you luck. Back ribs (at least the ones I get in commercial places like Costco, Sam's, supermarkets, etc always without fail turn out either awful or just "passable" for me. I actually have better luck doing them on a gasser. Go figure. Now, spares or St Louis Cut? A whole nother story. I almost always get great results on pellet grill and meh on gassers.
Now, if I get baby backs from the little shop in Arlington Heights IL (Thuringer) these turn out like the gods smiled down on me no matter where I cook them. I don't even bother buying back ribs any more as they leave me so discouraged.