Just use MDO and skip all the sealing and maintaince..
Lots of people swear by MDO. I haven't, but have heard enough to do so next time.
I'd still want to seal the edges.
I certainly swear by it now. I used 1/2" for my side boards and 5/8" for the floors of my 146DD. All I did was cut it to fit, use a router to round the edges and cut holes for straps (also rounded) to hang the floor from the frame and secure boxes to the floor. No sealing or treatment done at all. It is holding up great. I have one floor that has probably seen 80-100 days or more and while it has scratches and has faded a little, is nowhere near wearing through. The side boards aren't far behind that number of days and the same. My only complaint is it kind of smells funky when it gets wet...but it gets better over time. I think its the glue they use to bind it all together.
When I bought my 16' Avon it had plywood floors front to back and one piece broke in half and I had to replace it. I decided to do the Marine Ply and Spar Varnish route for that (this was before I tried MDO). I did 4 coats over the whole thing. It started checking on the first trip out and just isn't holding up like I had hoped. Feels like it would take a lot of maintenance to keep it nice.
So yeah... I heavily prefer MDO. Its not cheap, but its also not crazy expensive either. Similar in price to the Marine Ply I've found.
Does anybody know where to source 3/4" MDO in Grand Junction or Denver?
There are a bunch of places in Denver that carry it. As someone said, anywhere that caters to the concrete industry have it since they use it to make forms when they pour concrete.
I was unlucky the last time I bought it in that all the places that normally carry it for conctruction use had all sold through and had it on backorder.
My go to for weird plywood you can't find anywhere else is Austin Hardwoods, which is where I bought the last chunk of MDO for about $99 as I recall. It was either 5/8" or 3/4" 4'x8' sheet. I think the place that sells it for concrete use(but was out of it) was closer to $60 a sheet when they have it.
The other stuff I got I got from a friend that works for an Art transportation company. They make their crates from it and had a ton of off cuts. Unfortunately, the company sold to new owners and they were a lot more stingy about that stuff and that supply dried up. Like others have said, call around to a few sign shops that do outdoor signage. They use it heavily, and might have an off cut that fits your needs or could either sell you a whole sheet or tell you where they get it.
