If your stuck for a place for your tweeters. Heres what i made :-) :

http://www.clubpolo.co.uk/forum/index.php?showtopic=250151

You definately dont need rear speakers in a polo. In my MK2F coupe i have a Good spec Kenwood head unit. 6.5" kenwood components (quite basic, were only £70 new) in the front doors, running off a vibe litebox amp (fantastic bit of kit, tiny, and has never overheated) under passengers seat and an alpine 8" sub with alpine amp in the boot. Yes an 8" sub may sound a bit pathetic, but i have set this lot up pretty well and the interior mirror will dance to the extent its difficult to see in it when i turn it up. Its PLENTY loud enough and has impressed quite a few people with how good it sounds. I am thinking of upgrading the front speakers for better ones though :-)

ok just let me know and ill make one

yes 8's are fine tbh in a well made ported box they can slam even off low power, the dash tweeter is the better location for sound quality but still better than stock

i made a box for my 2.1 pc system using a 6.5" sub box tuned to 27hz that slams for what it is off 50w rms movies and music is great

i do like what you did there tbf mate, although i still have original door cards that dip in at the bottom :(

and id like the cabling the cabing to go through the door frame like on a modern car, just haven't had the time to sit and look how

i can also make the cards using your original card