I'd go with .5" Krezone, not sure what they call it in your area, but it's essentially Good 1 Side plywood with enamel paint, I don't print direct cuz I once shot one across the room when I forgot to raise my head height on my UV flatbed, I decal / mount with 3M IJ35C + matte lam
Crezon®, originally spelled with a C, was the grandfather of medium-density overlay plywood. The Crezon® brand name originally referred to just the resin-impregnated paper overlay, but eventually came to be applied to the plywood panel product as well. It was registered as a trademark in 1954 by
Dynea Overlays of Tacoma, Washington, an adhesive manufacturer. Both HDO and MDO were originally developed for the concrete industry to be used in making reusable concrete forms. The sign industry quickly caught on to MDO's usefulness as a paintable sign substrate. The Crezon trademark is "dead" now.
Many versions of MDO have been manufactured. The attached PDF is dated 2007 and lists Crezon® as a product made by Olympic Panel Products, Shelton, Washington. Note that Crezon is listed as the product equivalent of MDO Two-Step®, another brand name of MDO, characterized by a sanding step performed before the paper overlay was applied. Signal® MDO was considerd Olympic's premier MDO panel—it had hardwood plies directly under the paper and hardly any core voids, making it a good choice for flat cutout letters. Once painted, Signal MDO looked like 3/4-inch plastic. Guardian® MDO was the standard, no-frills (bulletin board) grade. I built my highway bulletins with it. I think it only came in 3/8-inch. MDO had a long run, over 60 years, as a sign substrate.
Olympic Panel was acquired by Swanson Group Manufacturing and the assets of Olympic Panel were to be moved to a state-of-the-art plywood facility in 2016 in Springfield, Oregon. That's where I lost the trail. Obviously, MDO is still manufactured and being used by the sign industry, as well as other industries. My 1960 GMC bread truck had a roll-up rear door made of 3/4-inch thick metal-covered MDO panels connected by hinges. Once, when the spring assist broke, I realized the door was heavy as hell. MDO is popular in the building trades, too, because it's paintable. It makes a good soffit material. And I'm sure HDO is still used by many state highway departments as a (low-cost) substrate for reflective signs.
Presumably, the MDO brands are still part of the Olympic family of brands.
Brad in Kansas City