There is a rubber grommet directly back from the battery on the 156 which goes through to the cabin just above the glove box. You will need to remove the plastic covers where the windscreen washers sit to get to it. Once fed through remove the glove box and feed the cable down the side of the car under the plastic trim.
^^^ the perfect spot. i ran both a 0awg and 8awg powerwire through the same area. plenty of room.
Thats not true,full range speakers will produce bass regardless of sub installation or not.
a 6.5" speaker is NOT designed to play subbass frequencies (<80Hz) LOUDLY. well, not the speakers for your doors.
loud, quality subbass depends on cone surface area, cone excursion, power handling/power available, and enclosure design.
even a long-throw 6.5" driver cannot produce the same doof doof that a 10~12" dedicated subwoofer can.
granted, top quality door speakers (eg: dynaudio, morel supremo, focal berillium, boston Z series, etc) are very good, so long as you fully seal the doors, sound deaden, and solidly mount their woofers. but these are relatively pathetic for subbass compared with even a cheap 10" sub.
but sure, yes, you can feed your door speakers 50Hz and you will probably hear it, so long as they're not playing higher frequencies loudly at the same time to drown it out. yet at the end of the day, there is NO substitute for a quality sub in it's optimised enclosure.
subbass is an important part of any music. it's not all about 'annoyingly loud' doof doof. you might prefer classical or jazz, and you won't hear the double bass through your door speakers.