I'm doing it! Finally.
Got some 2.1mm steel checker plate and I'm cutting it to size.
I figure I size it up, cut out slots for the rear roll bars to go through, then somehow get it in the to the right place, drill some holes, bolt it on - hey presto!
UPDATE: my grinder died, so it was off to Supercrap for a $20 one which did the job nicely.
Here's a few pics of where it's at so far.