The diff deflection calculation is easy Peter. Just by placing a straight edge across the new tool tray and deducting a quarter inch. The diff doesn't touch the original too tray so that's plenty of room. It's harder to estimate the width required to be honest, so that's a best guess. Diff deflection is about two inches, and there's a centre bump stop if you haven't noticed underneath the tubular hoop, held by two oversized bolts (just visible in the 9th photo). In fact I was toying with the notion of adding thickness to that 'bump stop' - it's more of a anti-knock strip to be honest. I'll line the inside of the tool tray hump with neoprene but I doubt the diff will ever touch it. The front bracket is stainless steel from my offcuts box and has some spring to it so should the worst happen, there will be a quarter inch lift on the front edge of the tray. The wooden cover is flexible enough to take that easily.
The wooden tray on my Roadster has slightly less clearance, and very occasionally under hard acceleration with a passenger, a bump will cause it to 'tap' the underside of the tray. The only time I had a real problem was in Kent with the broken rear damper when undamped deflection caused the axle vent to punch a hole in the bottom of the tray - now fixed.
