Never did like louvers on a Z or a ZX. IMO it detracts from the rear profile lines & just stands out too much. IMO rear louvers are best when they are actually incorporated in the factory body panels like the F40, GT40 or Maclaren F1.
I was also thinking about this today. It hit 87 in the shop. I have a spare hatch with louvres both in fresh paint. If I get my ac recharged I was going to test them out. The above pictures show a key point of reflecting the light. A white covering on the hatch carpet would work too. I put that white packing foam sheet over the dash when parked. I dont like the extension of body line either of adding louvres, but Im not afraid to be a little uggo for practicality like combating scorching vinyl. I purposely find shade or alternative vehicle to sit out in the sun. Then I got some cheap louvres and hatch, and having the choice of tint, louvres, or nothing/avoid driving. I opted for the do nothing answer so far. If I didnt have another ride, I would be using louvres and white dash covering. Tint can be removed without damage to defroster lines in most cases. Its not fast but you peel most of it off by hand in a sheet. And the repair kits, tint is repairable. Whatever the case if you are in the weather, its best to be equiped. 1 avoid sun, 2 be able to be equipped for conditions. Accessories are great, if they go on and off simply. Better to fight heat than bake.
To block sun, how about a retractable /spring loaded aluminum film type device? When the kids were younger, we had retractable window shades the used suction cups to attach to window. If the sun was shining in, the child could pull the shade down. It was made from a mesh material so driver could see through it. Why not a similar device that mounts to the inside of the hatch, uses the aluminum material, driver could pull it down or across when he parked? Or, same thing but with the "mesh" material and leave it up all the time?
veeeerrrry interesting....it does not say, though, how far it retracts out. I'm not sure though...how much this will help if the car is out in the sun for any length of time. Definitely better than nothing.
Hahahaha I do that all the time with my winshield cover when I park the ZX backwards. I drape mine between the passanger seat and my tool box and my emergency kit on the driver side. It gets balmy until I get down the road.