I would use upholstery vinyl that you can get at most fabric dealers. People use them to cover banquettes, kitchen chair seats, etc. It is vinyl on the outside, but has a mesh fabric on the inside. It is heavy duty and you can get it in different thicknesses, depending on what you need it for.
I was looking at it to do some mods just a few weeks ago at a fabric store. I think the heavy was $14.99/yard.
I googled "upholstery vinyl" and came up with lots of hits. This was the first one.Fabric by the Yard :: Marine Grade Vinyl Outdoor Upholstery Fabric in Black $9.95 per yard - Fabric Guru.com: Fabric, Discount Fabric, Upholstery Fabric, Drapery Fabric, Fabric Remnants, wholesale fabric, fabrics, fabricguru, fabricguru.com, Waverly,
I think using this fabric and a grommet kit, you could make your own at a pretty reasonable price, but it will add some bulk to your traveling storage.