I enjoyed doing the gag covers better than the story ones because they were usually simpler. A cover based on an incident in the plot took a great deal of staging to tell a little story that was still part of the book. And it had to make sense on its own.
I was proud of working 18 hours a day and sleeping three hours a night. It's something now that has turned into a problem for me: not being able to sleep... having insomnia.