I wonder how plywood compares to the typical welded steel floorboard, in terms of robustness? I’d guess a 3/4" CDX plywood would actually be more robust than the thin steel typically used, but it might have some weak spots where it connects to the rest of the car at the edges. Plywood isn’t going to hold up as well as steel to water either, but on the other hand plywood won’t rust.
Plywood is plenty strong, the Mosquito was built largely of plywood, one of the best performing planes of WWII:
2 Likes
I dunno. Even modern cdx plywood deteriorates if exposed. But I suppose if covered might fair ok. Roof and house sheathing is usually the pressed wood though but not exposed. Our camper floor was pressed wood but the underneath was exposed causing rot.
I subscribe to classic cars and often the folks curse the wood skeletons used in cars of the 20s and 30s. But I think they used solid oak or ash which would hold up better. Reminds me I need to put another coat on the trailer floor before winter.
Instead of the 3 ply cdx exterior plywood, a furniture grade, multi-ply, marine plywood was used.
Not cheap but the quality and durability is amazing with a higher strength to weight ratio than steel.
The bodies of cars from the late 1800s to the 1950s used wood to support tne metal bodies. Floorboards were called that because they WERE wood boards!
The Chrysler Airflow was the first all metal body in the US. The difficulty manufacturing the car caused one of the reasons the car failed.
1 Like
You can form ribs and ridges into the sheet metal to make it very strong and robust. Try doing that with plywood 
1 Like
The C4 Corvette had a balsa wood core layered with fiberglass as floorboard inserts. Not sure if the C5, C6 and C7 carried that along.