I ended up buying some adhesive deckgrip.
I was a cheapskate ..They had softer less abrasive rolls for $68 but they only came in black or white. ( I have one black board and one white to fix).
I bought the cheaper clear stuff c $18 but it's like coarse sandpaper.

Should be good for grip but it will probably rip your skin off clambering on.
I wonder if a slight sand with wet n dry would help?
I'm also wondering what it will be like to remove once it wears out?
I'm waiting for some sunshine to dry everything before I put any of it on.