Really depends a lot of things. Climate, number of mounting points, weight of rack, how heavy it is loaded and how hard the cruiser is wheeled. Obviously a rack mounted to the frame would support the most weight . Mounted to the body would do better if want to drill and add bracing. Then straight to the fiberglass which I personally would never considering the washboard trails in AZ. I personally would use a lightweight rack with a minimum three mounts per side. Unlike the frame the fiberglass top is not designed to flex, which would be a drawback if you wheel hard.