tony.latham wrote:Sande Plywood?
I just glanced at it on HD's site. It looks like it has the same number of plys as construction grade stuff -–plus an extra thin face layer that will sand through quickly. The fact that HD sells it raises a flag....
* I found two descriptions of Sande Plywood, so there are variations out there. Perhaps it's only Home Depot that sells the Sande that uses "not waterproof" adhesive? Here's the descriptions I found, along with the description of the plywood I used:

- Sande vs Arauco plywood.jpg (247.65 KiB) Viewed 1410 times
* When I was getting my trailer build started, I used an 18-20 year-old sheet of birch ply, topped with luan and polyurethane as my floor. Then I needed more plywood...so I went to a Home Depot nearest to where I was building the trailer (50+ miles from home), and found some sheets of 3/4" Arauco plywood sitting out front where someone had either not paid for it or was unable to use it. The stack of plywood had been tagged as $25 per sheet (about $10-15 les than the Oak ply I was looking for.
* I looked it over, saw the Arauco sticker on it, and looked it up on the internet, using my friend's smartphone (I only had a dumb flip-phone at the time, in 2011); I read that the plywood was made using phenolic resin (waterproof, even gasoline-proof...I used phenolic carburetor spacers while racing), and had minimal voids. I bought six sheets immediately (should've bought more, at that price).
* I used "the mix" of paint thinner and polyurethane to waterproof the wood, and covered it with TSC silo or tractor paint acrylic enamels (six coats of "the mix", pure poly, and paint total), and it has been waterproof for 9 years since done. I recommend getting waterproof-glued ply, and using "the mix". Use "the mix" even if not using ply with waterproof glue. It'll still stand up, I bet.