I drive a Demon (and not the other way around)

May not be possible at this time of year with the lack of sun/warmth outside, but if not, I usually use a heat gun at a distance on the backside to soften the carpet as I am working it, especially around the tunnel area and even more so for cars with 4 speed hump.

Regarding the radio wiring, I found these two articles, don’t know if they might help, but may be worth a look.

WIRING DIAGRAM FOR CLARION DB285USB - Fixya

Clarion db285usb wiring diagram - Fixya