Start by prepping the trim which is going to fit around the airbox. The trim should flare outwards as it gets wrapped around the air inlet. This is trying to form some sort of seal between the airbox and the vent on the side of the bonnet to pull in fresh air from outside, as opposed to inside the engine bay. The trim is a long piece of metal covered in rubber. To prep, use a screwdriver to move along the length of trim and open it up as shown in the pictures below, which makes it much easier to fit.
This will make it a lot easier to fit trim to the airbox. Note that my trim was a little on the short side, which will add to the PBC checklist, and would not wrap the full way around the airbox. The bonus of this was that it meant I didn´t have to try to wrap it around the very tight corner at the front of the airbox inlet, which is rather difficult! However I suspect this will need a longer piece of trim.
Next fit the airbox to the car. Screw the rubber mounts into place by hand.
Place airbox on top, I used M6 washers and M5 nyloc nuts of my own – no nylocs were provided in the pack, the manual showed nylocs and I figured this area may be prone to vibration. The washers provided in the pack also looked quite small and given the nut is securing plastic, I wanted the force to be spread over a wider area.
Now take the two metal inserts (these are wrapped in tissue paper and provided in another box) and insert them into the hose which connects the airbox and the engine. The short insert is for the end of the hose which connects to the engine, the long insert for the end fitting to the airbox, they won´t fit any other way! The manual talks about using brake cleaner as lubricant here, I opted for carefully applied force from a nylon hammer which did the job fine. You want to get it inserted past the top and it takes a fair amount of effort, don´t stop with it flush with the top of the hose.
Now fit the hose to the top of the airbox, test fitting by checking the angle. This is not a precise fit and requires some wriggling to get it into position.
Once satisfied with the angle, make sure you place the filter into the airbox and add the large hose clip to the end of the air intake hose (where it meets the engine). Put the lid on the airbox and secure using the screws from the pack, using the plain washer and split washer, as usual split washer is closest to the screw head. The lid can be a fairly tight fit. Finish off by tightening the hose clamp to the engine.