Ok I had another go at my under tray tonight. Not quite finished yet, got to make some pressed covers to go under the wishbone cut outs and cut more holes into the rear outlet panel and a few other tweak's.
I've created a slot at the rear above the strakes to allow some of the air to be released from the rear tub area, I guessed it might help.
I took Phil's advice and was hoping he was going to post his revised drawing (why did his original post disappear) so I took a stab at it on my own.
The angle at the rear is about 12 degrees and the whole assembly is made from 2mm aluminium.
Well that's it for tonight...cya.