Bark comes from heat. First of all DON'T skin or trim that picnic!!

If you start your meat at 400 plus degrees and let it cool to your cooking temp, you'll get bark on it. Slow cooking doesn't let you make bark unless you make it with the rub and that ain't bark, that's crust.

I take my butts and put them in a cooler and season them the evening before I'm going to cook them. I have an indirect smoker like a Texas style with a side fire box. I cook with pecan or some kind of dry seasoned wood. Start your fire and let the grill heat up to 500 or 600 degrees. Load the meat and close it up and my grill will come back up to 450 500 and I cook for about a half hour at that temp and then let it cool down to 300 or so to cook it the rest of the way. Usually takes 5 to 6 hours for large butts and that picnic will take less. When the butts are 160-170 inside temp I take them off and put them back in a cooler to set for a while. The internal temp will go UP to 180-190 and then the meat will relax. Usually a couple hours or more. This rests the meat and will let it just fall apart and you'll still have bark on the outside. Try it........