Thanks. 2 bits of 600x900mm 1.5mm NS4 from Merlin motorsport, a bucket of closed end 5mm rivets, some sikaflex and a jigsaw with a fine metal cutting blade.
Did think about just a single panel on top, but this is (pretty much) flush, has the centre bracing bar to stiffen it up too and it's just smarter to have flush panels with sequenced lines of rivets.