Plywood Cart Design

[Arthur Wood]

I'm building this lumber rack and plywood cart design from Shopnotes #17.

(pic attached)

However, I'd like to make one design modification. The swing out card as pictured is aligned horizontally. For space issues along this wall, I'd like the cart to swing out vertically (i've got sufficient space for the lumber rack above).

Any comments on how to make a vertically-oriented plywood cart stable enough (minimize sway).

Thanks