I've got a 20x40 offset with an expanded metal rack. I used to just brush them real well once the smoker got up to temps but lately (after reading some of Myron Mixon's book) I've been smoking in the disposable aluminum pans. I was initially worried that it would result in softer BBQ and I'd lose that char-tastic burn you get on the bottom from grates. Now I'm officially a fan and wish I'd thought of this sooner. It makes cleanup much easier and I can't tell a difference in the Q one bit.
Bowl Bound and B-B-Q-in! Sic Em Bears!