I have seen a vinyl decking that would do the trick.
But for the life of me, I can't remember the name of the MFG.
The deck is installed by screwing a track on to the joist and then snaping the deck boards over it. It is very ridged and will span 24"oc.
The deck boards the I have seen are 5 1/2" wide X 1 3/8" tall.
I will take a photo of it and send it to you.
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