BTW, my DAB+ antenna is one of these hanging in the rear window. Works ok 95% of the time, but still thinking of doing an external one.
I used a 7" Joying android in mine. It has detachable screen, so I located the head unit under the passenger seat, and used a 100cm cable from Joying to connect the two together. Line outputs feed the door amps via 5 balancing transformers that sort out any noise & hum, plus give the required signal boost passively.
Most Chinese androids run too hot, so I also added a 12v fan using a 9V feed to keep it cooler. Mounting away from heater also helps !!