Re: NO LBC - trailer 5' x 8' decking?

I would check either Weyerhouser or possibly Murphy Plywood in Roseburg, OR.
You might also try to buy some from the trailer manufacturer, or find out
where they order from.  It would almost certainly be a special order item,
and unless you have a use for a few train car loads, it might be better  to
improvise.
Kate