Just an FYI that we have found that small butts like your 4lbers tend to take an abnormally long time. In the future I would strongly recommend using 7+ lb. butts. I would get them in the smoker asap if you want them done by dinner time.
Regarding using trays/drip pans, they can cause issues with your temperature controller's ability to accurately hold temps. So, my recommendation would be to use the smallest possible drip pans should you decide to use them.
Good luck with your smoke.
By the way if you didn't brine your butts, I would encourage you to check out Divotmaker's pork butt brining post that is set up as a sticky at the top of the pork section.