Car audio. i just bought a jvc KD-G431 but could not install into a vauxhall corsa 2004 as the

Question

i just bought a jvc KD-G431 but could not install into a vauxhall corsa 2004 as the wiring at the rear of the unit is too large and now have to put it on the bottom tray which means i cant put the facia in. Any ideas am i doing it wrong?