I know this thread is old but just stumbled on it.
Although we just sold the cub camper, I'd welded up a custom roof rack from 25mm box steel and angled the "skids" to fit in the gutters of the fibreglass roof. They were then wrapped in foam tubing to protect the roof. The racks were removable so as not to place undue stress on the winding system. Two very short rachet straps were used to attach it down the sides of the van.