I'm hungry...

The next step in the spline joint was to cut 7/8" strips of 1/4" OSB that will be glued in the slot cut in the facing edges of the plywood. I used OSB because I couldn't find 1/4" plywood. The only thing Home Depot had labeled as 1/4" plwood looked more like thinly veneered particle board so I figured this OSB would be stronger.

After dry fitting my strips (pictured above) I ran a heavy bead of glue down the slot in one piece of plywood. Then inserted the OSB strip so the glue oozed out everywhere making good contact with all surfaces. Then I ran another heavy bead of glue down the slot in the other piece of plywood.

Then the fun began! Working alone in the shop and trying to manipulate two 8'x4' pieces of plywood together wasn't exactly easy. With the help of some ratchet straps and my hammer I got them to fit snugly and most of the glue wiped up from the top side at least.