I wanted such a net as well. I purchased on a closeout sale the exact Porsche product that you have. I'm not impressed with it. The net is too small, so when stretched to the point you can anchor it at all four corners, the tension pulls the mat off the bottom-side embedded support rails. You'd need to substantially load the mat to prevent this, but then I'm wondering if a) you'd be able to stretch the net sufficiently to anchor it, and b) would the tension be so great as to pull the anchors out of the mat?
I come from VWs, and VW makes a
cargo block that I plan on purchasing along with a trunk mat from
Lloyd Mats. Other companies make similar products.
The only other option I'm aware of is welding some anchor points into the trunk and sourcing/sizing your own net.