Brisket or butt, I get my bark the same way. I use a mustard slather and my rub is typically 1/4 to 1/3 sugar. Cook at around 225* for as long as it takes. I'll spray (really more of a mist) with apple juice at what I guesstimate the mid-point of the cook-time will be and only after I'm sure the bark has set-up. Does no good to wsh the rub away. I do not foil while cooking.
I pretty-much always get good bark