So we are quickly approaching year 3 of Model S ownership and it's always been a goal to try and make the rear facing seats as comfortable/useful as possible even in the hot summers. One would think that Tesla does not care for the well-being of it's 3rd row passengers when you look at how inadequate the default HVAC setup is (turn on fresh air setting, crank to 11). All that being said, ceramic window tint + the rear window shade takes care of blocking most of the heat coming in, but circulating air back there is still an issue. Enter stage 1 of my latest Tesla project. Using a couple different fan templates, I was able to 3D print an adapter of sorts that holds a standard 60mm computer case fan and mounts directly to the car using the stock plastic trim pins and no drilling/cutting/or other wise mutilation to the car. Then I printed a 60mm 90' vent/tube to direct the air straight into those sweaty faces. The current version is a little on the rough side, but it does the trick for testing. I'm using a couple of fans I had just laying around, however the final version will have 2 Delta fans that claim they can move up to 40cfm a piece. These current placeholders can do almost 20cfm, bless them. I don't have the upgraded audio package, so these fans will mount directly to the area where the rear hatch speakers would have gone. I'm currently trying to figure out the best and most tasteful way to install the grill cover back on. Unfortunately this setup will not be completely stealth, but I still think it can be done tastefully and look professional/stock The rough idea here with regards to airflow is first and foremost just getting the air moving back there. But the design of the rear hatch trim panels allows for a small bit of air to be drawn through channels on either side underneath the trim that lead up to the panel where the hinges are and consequently right where the cool air from the main cabin gets stuck. However, slots would need to be drilled in that trim piece to open up that source. The headliner would hide the openings for the most part. We will see how the upgraded fans function with both setups, but as for now, this looks to be a very good start. Stage 2 is even more exciting because it would involve one or two 120mm x 40mm radiators in that same front trim piece with hoses run from the front of the hatch to the rear where 1 or 2 peltier coolers would be sandwiched between a liquid cooling block and an aluminium heat-sink. The idea there being that the fans would be drawing air up that is chilled as it passed through the heat-sink. I'm currently building this setup outside of the car to test and tweak, but from experience, as long as you can dissipate that peltier heat, those pads will get very very cold. But now for the kicker. Unlike other setups that are required to be battery operated or hooked into the cigarette lighter socket, both of these are relying on the already existing 30amp power source in the rear hatch which is completely unnecessary in the summer.... the defroster. Which of course, wait for it, is controlled by the touchscreen. So this setup is nearly stock in it's interface with the driver; just press the button and the system comes on. A simple 2-way switch in the hatch can change you between "Summer" and "Winter" mode for the button function. And while the fan-only solution requires just a couple of amps, the peltier option would still come in at a reasonable 20-25amps depending on what pumps and what cooling plates were used. All well within spec for load and safety.