I have stayed in those same parks in May and the temps were high 20s and low 30s for a few hours at night. Never did anything and never had a problem. I have chipped a little ice in Minnesota to disconnect a water hose in September and never had a problem with the lines freezing. A fresh water tank is a lot of water as are the black and gray tanks. It would take a long time for that much liquid to freeze at temps only slightly below 32F. Pipes are mostly inside in most units and are going to retain the ambient temperatures for quite a while. You probably will be wearing short sleeves in the daytime.
Paul