For a cookoff or big catering I hold the hot butts wrapped in foil in the hot cooler. Once you pull the pork it starts drying out fast.
For smaller jobs, you can foodsaver it quickly, cool it down and heat it later.
Last but not least, after pulling and during holding you can wet it down with a 50/50 mix of apple juice and barbecue sauce. I mix it and keep it in a squeeze bottle, and use as little as possible as needed.