I ordered one too last week after it had been out of stock for a couple of weeks. Received it earlier this week but haven't had a chance to use it in the car except for a test fit.
I agree with
@SmingusDingus that it fits perfectly in the subtrunk with room to spare around the sides for ventilation. I tried it out in the house setting it to -4F and it got down there within an hour or so. I checked with an separate thermometer and it got close to 0F but would have probably gotten down to the setpoint if I left it running overnight.
The cheap price with the Costco return policy is a winner.
Got my Costco Phantom 30L cooler last week. So far, opinions are pretty positive.
As I mentioned before, in the five seater, there's actually a slot/gap under the rear of the subtrunk cover that serves as reasonable ventilation for the fridge. So you can sit the subtrunk cover flush over the fridge while running without any worries. As far as I can tell, it does not get excessively warm in the compartment and the fridge seems perfectly capable of cooling itself to any desired temperature with the cover in place.
When the fridge is in the subtrunk, there's still space on the left side for one bag's worth of something. Ventilation for the fridge is on the right side, so I'd lean towards leaving that space clear.
I run the 12v DC power cable out through a small gap in the outermost corner of the cover and into the 12V socket.
Temperature settings are remembered whether the fridge is plugged in or not. There is no smartphone app to control or monitor the fridge.
I tried to get clever and power the fridge via a USB-C to cigarette lighter socket. Unfortunately, the fridge has both undefeatable low voltage cutoffs to protect ICE car batteries and a starting amperage that is too high for lower amp USB-C settings. 15V/3A adapters supply insufficient amperage to start the compressor, and 20V/5A is interpreted as below the low voltage cutoff for a 24V battery, so the fridge errors. It would take some more serious hacking to work around this, so I'll just use the supplied DC power cable ... it's not a big deal.
Today, I was able to fit a 2 gallon pack of Costco milk (in the square jugs) plus a relatively flat bag of frozen ramen. There was room for a bit more on top ... perhaps another relatively flat bag of food. The compartment is quite deep.
OK, you're not going to be stocking up on frozen pizzas with this thing, but it can help extend a day trip of errands if you compromise a bit around it. If you're stocking it purely for a trip, you'll be able to pack it with a lot of stuff.
I think there's still room for a custom fit fridge that really takes advantage of all the space in the subtrunk. The one coming out of China right now is quoted at 35L, which doesn't seem like enough of an improvement considering it fills the entire space.