My son is doing Custodial this semester at Epcot. Not sure about clothes under costume, but it is very easy for him to change into a different shirt at break time so he can eat in the park if he wants...ie right now since it's food and wine festival. The can liners are never very heavy because there is a pretty constant rotation of changing them. He was iffy about custodial, but has come to enjoy it. He likes the freedom...you're on your own...He likes street shifts for the interaction with guests...takes pictures, gives directions, trades pins...and he actually enjoys restroom shifts...I think mainly because they are way easier than you could imagine. Alas, I speak from the other park...perhaps someone can give you their thoughts from DL. Good Luck, and have fun.
