I want to install a composite deck (probably EON) over an EPDM
substrate.

Since puncturing the surface is out of the question, I plan to glue
sleepers to an EPDM pad which in turn gets glued to the EPDM surface
with rubber-to-rubber adhesive.

I've seen Wolmanized lumber used for sleepers, but I don't trust it not
to warp and twist unless seriously screwed down, which can't be done
here.

So I'm thinking - why not a composite dimensional 2x, since it should be
dimensionally stable enough to glue down and stay put.

Is there a composite that I can use for sleepers to screw deck boards
onto?