Well guys, that went really well.
£187 plus vat with free delivery for the full set of air bags from Island 4x4 and 3 hours trouble free work and the air bags are done.
The system took a while to sort itself out when I had finished, the fronts weren't raising to top lift but after 5 or 6 attempts they got there and now it seems to be working perfectly.
Now all I need is to see it still pumped up in the morning!
Thanks again for your help and advice.