Originally Posted by BBQ Bandit
Boil in a bag is the best option for moisture retention.
I like this idea. If you just have a kettle and an aluminum pan, vacuum seal the whole brisket once it has cooled a bit (or you will steam it), then when you reheat, put water in the pan on the grill (big enough to fit the brisket in comfortably, like a disposable aluminum turkey pan), put something in the pan so the brisket in the vacuum seal isn't touching the bottom of the pan but so water is still surrounding the brisket (for example, a cake rack), and gently boil it back up to temp (you may have to flip it a few times), remove when it just begins to steam in the bag. I think that would be your easiest way. I wouldn't slice until after reheat this way. Brisket (and any other meat) begins to dry out once it is sliced.
Good luck. Let us know what method you went with and how it worked out.