It rained the day our pool was shot. The builder covered the site with a gigantic sheet of plastic and poles. Then, once they were done shooting and forming the shell, they just dropped the plastic down over the shell and weighted it down around the edges with the rough grading material on site.
You're supposed to water cure the shell, but we didn't have to. The builder said the plastic would retain the moisture. They just told me to keep an eye on it, and if I didn't see condensation on the inside of the plastic to just spray the garden hose underneath the plastic until wet. The next crew that came out after the cure removed the plastic and it was perfect.