If you are thinking of having a cover made or making one I recommend using Noah Fabric from Kimberly Clark. It is a light, strong, soft, breathable fabric. It has a soft inner layer bonded to a strong outer layer and a layer of breathable but waterproof material. It is used extensively for car covers.
I picked up a van cover that gives a fair fit to my trailer. No need to pad the corners of the solar panel or other edges. I’ve had it for eight or nine years with no sign of deterioration. It is light gray and allows enough light to pass through for the solar panel to charge the battery over the winter.
The cost per yard, 55” width, is $15 US, 40% cheaper than Sunbrella.
https://www.fabric.com/buy/0742668/4...er-fabric-gray