GPS - the internal antenna works fine inside a car (the original deployment scenario) when the bag is sat upright on a passenger seat (which is the preferred orientation for best cellular signal acquisition). It also works when wearing the backpack of course out and about. I did think about adding an external GPS antenna connection, and even knocked up a custom antenna RF switching PCB to enable the choice of internal or external gps connections with a latching button press but I ran out of time to thoroughly test this so chickened out.
Heat - yes the Transits run hot. The thermal design includes vents top middle and bottom to encourage convection and multiple internal panels designed to increase surface area and conduct the heat away from the Transit. The preference is to run it with the top of the bag unzipped, but even with it closed - in UK climates at least, the top of the enclosure consistently sits at 19-20 °C (the bottom runs a little warmer). I have a newer prototype with active temperature controlled cooling on the workbench at the moment where I have butchered a laptop cooler to exhaust hot air from the top of the bag with a vent cut into the bottom. However in this initial deployment the customer (a high worth individual) wanted to choose their own bag (I suspect my ‘amazon special’ wasn’t visually appealing enough).
XLR DC power - yes you’re right, it should be 4 pin, had a bunch of 3 pin XLRs kicking about so used those on this build for the sake of speed.