Matt- Dont use plywood unless it is marine ply. I use 1" thick pine boards. My first batches of deeks were made with drop clothes and they worked out fine, as long as they are canvas. I typically get a bucket of hot water and wet out the canvas before stretching and stapling it on the frame. It "gives" a bit and stretches really tight. Let the canvas dry up, otherwise the water and moisture will mess up the foams expanding properties.
Good luck, post a pic of your project.
Derek
Good luck, post a pic of your project.
Derek