Like Harditrim XLD 1" or 3/4" Smooth Plank or Harditrim HLD 3/4" Smooth Plank, Dan.
If the 1" XLD was used, I don't think I'd even metal wrap them; if you're familiar with Hardie products, you know how stable and weather-resistant it is & how well this product will hold paint.
I might wrap the 3/4" HLD just for some additional rigidity, unless you had a vertical "stringer" on the center of the backside of the panel, but an 8" plank 30" long is still quite sturdy on it's own.