Fairly easy one this. Remove glove box and you'll find a knock through section on the back about the same diameter as a pound coin. Knock this out, no subtlety required.
Then fit the glove box vent within so the external inlet pipe points upwards. Push it firmly home, it will just click in.

Inside view

Now locate the ac feed pipe Vauxhall have provided, top right of foot well, rear of centre console, above the footwell vent. Screw driver in the back ground shows general location. Your looking to remove the rubber cap shown in hand. A coat hanger wire with a hook bent over on the and helps here, and fit the end of the feed pipe in its place. Fiddly this bit, unsighted, feel your way. There is a bit of moulding partially obscuring line of site, but it does go on.

More detailed closer pic of the outlet with cap removed.screw driver shows exact location.
