Well I have now done the front speakers.
I used a 90w RMS (400w) freecycle amp, £15 worth of speaker cable, my old speakers, £15 of adaptors, and about £7 of power cable.
Amp lives near gas tank, speaker cables run back along sills, into the A post cavity at the bottom and pulled out into the door hinge area by the cable grommet.
Then fed into the door, via the cable connector area - there is a small gap outer top which speaker cable will squash through.
Fed it downwards, wrapped around a bracket for the window then back out via the hole where the cables come out.
Left original speaker cables loose. Fitted the cross over inside the arm rest, chopped out a bit of polystyrene style filler. Used my hot glue gun here.
HGG the tweeter cable to the panel and HGG the tweeter into the door panel grill.
I have not touched any of the Vauxhall loom so if I wanted I could return to standard with out too much work.
I tested for 5 minutes, definately clearer, managed to drive the speakers near to their limit rather than have the amp head unit struggle, bass is better controlled, will find out on the way to work how good it is.
Only weak spot is the amp, may need replacing - but I'll leave it as is for now.
Two main problems, one was finding a route to the doors, research took me about 3 hours in total. The other was removing the window switches - they end up dismantling themselves.