Okay, because I'm a total dork, I found an old t-shirt and slept in it for a few nights before I left, cut it in half, then put half in each cat's crate. It made ME feel better even if they didn't care about it! The people at the airport asked if I wanted to give them each some water. I did, and in the end one cat ended up peeing in the crate. The other one ran to the litter box as soon as we got in the door! Like Zeusy, they cleaned up the wet stuff in my cat's crate and put it in a plastic bag which was thrown away at the next rest stop!