you sound like the man w/ the plan...
The French cleat is a great idea, wish I'd thought about it when I did mine - taking it down every 2 -3 years to wash the (vinyl) lattice and power wash the deck is a major PITA because of the number of panels (3) and all the trim pieces and joiners. I have to stick little pieces of masking tape on the parts so I can get them all back in the same location. You can't tell from the photos, but the bottom piece - below the horizontal trim piece - is separate, added to minimize the gap at the bottom. This was done so I could use just two sheets rather than 3 with a lot of waste - the track saw came in real handy for cutting those narrow pieces off the sheet. With the French cleats, you're still going to have to attach the "frame" to the deck so it doesn't blow off in a high wind.
This is such a good idea! Being the unimaginative sort, I'd never thought about using french cleats for anything besides hanging tools in the workshop, and hanging heavy picture frames. Good luck, and we'd like to see some pictures of your progress.
Can you screw a 2 X on edge under the deck boards then add another deck board on top of this around the deck like a picture frame?
