I use a couple of different methods. For vacuum-packed pulled pork, the boiling method works well. For whole pork butts, I vacuum pack them while still wrapped in one layer of foil (holds all the juice in). Then, I thaw in the fridge for a couple of days, and put the foiled butt in the crock pot, on low, for 4-5 hours. I place a round pie rack under it, so it's not sitting on the bottom of the crock pot. When you unwrap it, it's perfect! I then pull it, as normal, and place back in the crock pot on "warm." Covered, it stays nice and hot & moist for serving.
For ribs, I cut my full racks into half racks, and vacuum pack them for freezing. Again, thaw in the fridge a couple of days. Since it would take a big pan to boil half-racks of ribs, I use the crock pot for them. I have an 8-qt pot, so I can stand up to 4 racks of baby backs in there. I put them in vertically, sitting on their sides. I'll put about 1/4" of apple juice in the bottom, cover, and heat on low for around 4 hours. Again, they come out moist and hot.