I have the older version #2 and when I smoke butts, I always do 4 of them to save on time etc.. This past weekend I did 4 of them, 2 10lbs and 2 8lbs. I have never had any problems with the top drippings being too much on the bottom.
Two things to watch for: If you use a water pan, don't put very much in it as the drippings from two will put a lot of juice in it. I put very little in my water pan and at the end it is almost full and my catch pan is also.
Stagger how you place them in the smoker so the heat will distribute evenly between them.
When I do 4, I place the two biggest ones one up from the bottom rack and the two smaller ones one down from the top rack and they usually get done within a couple of hours of each other.
I am a firm believer in the temp probes being in there though. I usually put mine on at Midnight and go to bed and have them done between 12 to 5 the next day.