I'd use buffalo board it's very high quality weather resistant ply with a tough, durable non slip coating on the front / back. I've used it the past for all kinds of applications including boarding out my old trailer bed and it lasted years sat in wind/rain/snow when not in use and being heavily abused when in use.
Looks like it would work, but heavy if the thinnest they do is 9mm, which is probably overkill given the spans and loading. Also couldn't find a vendor near me, so that'd add 30-50% onto the price.
I'd use buffalo board it's very high quality weather resistant ply with a tough, durable non slip coating on the front / back. I've used it the past for all kinds of applications including boarding out my old trailer bed and it lasted years sat in wind/rain/snow when not in use and being heavily abused when in use.