I use a router for ALL kinds of building processes for boats and guitar-building. HOWEVER, putting an edge-bevel on a 16ft. 1/8" thick length of plywood is NOT the job for a router. It's just too easy to run a 30,000rpm router bit right through that carefully-lofted panel.

As Chip pointed out at the beginning of this thread, sanding or planing a bevel on the edge of the plywood will give you a very easy to see visual reference. The various layers will show how much you're taking off, making it a breeze to make a consistent bevel. A sharp block plane or 50-60 grit paper on a firm block is all you need to make that inner bevel. It should take just a few minutes per panel. Just bevel the edge to the outer wood layer of the plywood. You do not need a bunch of jigs to do this. Try it on two pieces of scrap plywood and you'll discover how simple it is. Focus on a consistent bevel and don't sweat the actual angle. There's nothing special about 45 degrees, anything from 15-20 degrees to 45 will be just fine.

I have seen a few instances where the builder chose not to bevel the inside edge of the panel and just stitched them together with the inside edges touching. It made for an interesting AND attractive look with the epoxy/wood flour fillets on the outside creating a dark pinstripe between the panels.