The choice of material is essential if you make covers by yourself:
The fabric shall be made of Polyester as if does not degenerate due to UV-light as quickly as other fabrics, Nylon is a big NO for long term outdoor usage. The water barrier(in the fabric) shall be PU, it is cheaper and more common with PVC barrier. PU will last longer, PVC will start to fall apart after a year of two.
you also need some kind of lining to make a barrier for condensation, the old school is std cotton, works fine but is kind of expensive. I found knitted 3D-mesh in polyester (equivalent as clouddancers hail proof lining) to be both cheaper and better but also bulkier and heavier which is to be considered during handling and transport.


This is what I used:
https://www.profabrics.co.uk/product...ant=6809802627
https://www.profabrics.co.uk/product...ant=5940965187
https://www.profabrics.co.uk/product...esh-lime-green