I had this large sponge type thing that was part of a kiddie pool, that I used when traveling. It would fit in the bottom of the suit case perfectly, It was about 24 inches long, and about 20 inches wide. I used one of those giant zip lock baggie things to transport in. I would take one of the hand towel and cover her in the tub while bathing.
Also I have done the shower method, I would get in take my shower, my Mom would hand me the Baby... wash, rinse, snuggle, kiss and hand him back out to my mom all done...