This is what I do for 8+ hour holds meat stays solidly above 140 the entire time.
Double wrap everything in heavy duty foil. Do not allow for much time outside of the cooker or cooler. Pretty much you want to (double) wrap it and get it right into the cooler.
I line the bottom of the cooler with a towel, or several, depending on size. I then pour boiling water over them. I do this until they are wet, but not saturated. It definitely creates a lot of steam. Try not to leave the cooler open unless it's to add or remove meat from this point. I then add my meat one at a time, pull from cooker, wrap, right into cooler. Make sure the extra space is filled in with more towels.
\m/ Heavy Metal BBQ \m/