Hey 555
I cant really advise you.
With my son we just copied an existing board.
I made a nice fat board laminating the deck to give rise at each end allowing for a lower deck. Hit it with the planer to get required thickness and a cool effect
Achieved width wise concave with strips of ply. so no science from me.
Cheap bunnings 3 ply veneer x6 sheets. Aquadere exteror glue..
didnt really expect much,, it was a proto for using beter materials.
But surprisingly it seems ok so far..