[QUOTE=tangledweb;6902746]
I’m sure you’ve looked harder than me, but it does seem like it’s hard or impossible to find.
A quick google shows very long is possible, but nobody in America seems to go wider than 5’. I thought plywood was as American as apple pie. I wonder why you can get big single sheets in Australia, Asia and Europe but not here.[/QUOTE]
Yes. I’ve called several custom lumber yards and they have all said they have never seen or heard of a sheet that large. The second best alternative to the one piece floor would be two 4’x12’ 1" marine grade sections biscuited and glued together with a single reinforcement bar welded from front to back center on the trailer. Then, bolt along the sides and on the middle reinforcement bar. But even this is something I haven’t been able to source.
The third option is three sheets of 4’x8’ 1" marine grade biscuited and glued together on the long edge with two reinforcement bars welded across the floor of the trailer where the seams are. Bolt on the edges and along both sides of the seams. This would be the cheapest option by far as 1" marine grade ply is going for $70 per sheet.
The downside of trying to fabricate the floor from multiple sheets of ply is possible separation and subsequent rot at the seams and flexing of the trailer working those seams apart. The floor would not be as solid as a one piece.