Hello Peter an Ann,
I concur with you that a grab handle should be fit for purpose, and allow you to manoeuvre a caravan without causing damage to panels.
I am an advocate of customers asserting their rights to expect goods to be fully satisfactory, I also advocate that customers should be reasonable about how their difficulty is resolved.
If the fault is unlikely to cause longer term issues, and it is relatively easy to repair, then it is likely to be unreasonable to expect a complete replacement or refund. I think that a cracked caravan panel which can be replaced without further internal damage would fall into this category.
Where the panel has been allowing substantial water ingress, that has affected the internal wall structure, and frames, then the situation is more serious.
As with all such claims, each one should be judged on its merits.