The bag in water method works great. Also, you can put about 1/3" of apple juice in a crock pot, dump it in and reheat on low for a few hours. If you have a whole butt you want to reheat later, the best way I've found is to double-wrap in HD foil, just like any other time you take one out of the smoker. Then, let it cool awhile, and vacuum pack the foil wrapped butt for freezer or fridge. When you want to reheat, thaw the frozen butt in the fridge for a few days, then take it out of the bag (but not the foil). Put the foiled butt in the crock pot on low for 4-6 hours. When you unwrap it, it tastes like the day it came out of the smoker! Did one like that yesterday, for my folks at work. Perfect!