Interesting advice from the supplier. I spoke to someone who converts vans and he said in his experience the flexi panels fail when there’s no air flow underneath as they overheat. He also said it happens more with black pop tops, as they absorb more heat.
Mine is black so I’ve decided to go for a rigid panel this time and remove the old one.
The rigid panel has a 5 year warranty whereas the flexi has 3, and the rigid is half the price.