When I do foil wrap, I always wrap tightly in 2 overlapped sheets of foil. As you mentioned, I think your real issue was the low cooker temp. I usually crank the heat up on the smoker after wrapping, since the meat is protected more from the higher temps. I've even moved it over to the oven a few times after wrapping, since it allowed more control of the heat and with the foil it's not going to pick up any more smoke or flavor from the smoker.
My last brisket I switched from foiling to using butcher paper to wrap it at the stall. Saw this in a video from Aaron Franklin from Franklin's BBQ in tx:
http://video.pbs.org/video/2365494916/
Came out awesome, and kept the bark much more firm compared to foiling.
Haven't tried the butcher paper on a pork butt yet, but I'll definitely always use the paper on brisket from now on.