My installation is very discreet. The DVR itself is hidden inside the map reading light compartment with the lens fixed onto the rear view mirror using the 8 inch lens extension cable and a thin piece of wood painted black. Initially I used double sided tape to mount the lens module onto a thin piece of wood, but it was not secure and I find the lens detaching from it all the time. I resorted to hot gluing the lens in place and this resolved the issue. With this setup, I am able to view the LEDs directly to confirm that it is recording. It's probably not the most elegant solution especially with the hot glue, but it's probably as discreet as it could get.
I've been using the Mobius for about 2 months now and I've not experienced any issues with overheating, but then again, I'm in the UK where temperature rarely gets above the mid 20 degrees C, even during the summer.
Perhaps one day I'll make a video explaining my setup along with the wiring and 12V - 5V conversion.