Dave,
If I do whole butts for warming later (office, or whatever), I double-wrap in foil, as usual, when removed from the smoker. Then, I let the wrapped butt cool a bit, and seal the whole thing (still in the foil) in a FoodSaver bag. To reheat, I put the foiled butt in a crock pot on low for several hours. When you unwrap it, it's just like a fresh, rested butt! Pull it onsite, and they'll think they just got one right out of the smoker!