I ran across a cargo net for sale on eBay that claimed it was made for the 370z.
Link is here:
ENVELOPE STYLE TRUNK CARGO NET FOR NISSAN 370Z 2009-2016 09-16 2015 2014 2013 | eBay
Ordered it to check it out and it arrived yesterday. Unfortunately, although the price is right -- the part I was sent doesn't seem to be! It's actually longer on one side than the other, vs. being an actual rectangular shaped net like one would expect it to be.
I can't figure out any possible way to mount this net that doesn't look lopsided.