put it right on the grate- I know you dont wrap it in tinfoil but do you put it on something (wood plank)?
Never smoked haddock but my fish brine is about 3 parts brown sugar to 1 part kosher salt or abt 4-1 pickling salt. You can add garlic or herbs, whatever makes you happy. Pack it on dry for 4-6 hours. Rinse and let dry before smoking it. I just put it skin down on the grill but cleaned well first.