I have flexi panel and your right it is unsupported between the ridges, but I think those ridge gaps actual help the panel to remain cooler with air flowing along the gaps between the ridges. Mine has lasted nearly 3 years so far fingers crossed.Is the problem with a flexible panel on a PVC roof is it is unsupported between the ridges? I would have thought they were only suitable for smooth surfaces, either flat or curved, which can fully support them.