Make my own Kick Panels?

A trick Russ Meeks taught me some 20+ years ago is to use 1/8" mahogany veneer for making up interior panels instead of some form of cardboard or fiberboard.
It's easily cut to size, stable, and you can weatherproof it with a couple if coats of spar varnish, and it holds glue and staples well when attaching your upholstery material, especially when folding it around the edges and stapling on the back side with short staples to hide them.
You can find it easily at the home improvement big box stores as door skin, but I've found it was usually cheaper to buy it in a 4X8 sheet.
ABS sheet stock also works well for doing interior panels when you can find it. It can be shaped, molded, painted, and allows you to skip adding fabric entirely, although gluing fabric to it is an option.