I took some pictures of my mystery rack. Understand, it's been on there for 4 years now with the Kuryakin Bag on top and no issues with the trunk lid cracking. And the bag is full with soft stuff as mentioned earlier.
So yea, I would agree that having metal straps braces underneath is good...I never bothered to do so.
On the pictures underneath the lid, the rack bolts are the small ones on each corner of the picture!
David