2m length of 67mm Internal diameter straight exhaust pipe (from motor factor) £18
Some scrap curved exhaust pipe sections
12 inches of flexible hose (from agricultural store) £3
Mushroom (from agricultural store) £20
2 jubilee clips
150mm x 40mm x 3mm flat bar
2 M6 nuts, bolts and washers
I modified the standard oil bath filter. It was quite fiddly as it's made from 0.5mm thick steel. Note that with a standard engine it would make more sense to have the inlet port inline with the outlet, but my engine is from a Transit. The snorkle is attached only by the flexible hose and a steel bracket bolting to the roof gutter - very solid. It is possible to buy short curved sections of exhaust pipe, but they were £20 each, so I got some bits of old exhaust from a mate.
A good tip for finishing the edge of the hole through the wing is to cut a length of small diameter rubber pipe to the length of the circumpherence of the hole in the wing, then make a slit down the length of the pipe, and push the rubber hose onto the edge of the hole.
For greenlaning it's good to not have the snorkle protruding from the side of the vehicle as it's likely to get knocked on trees and rocks, but the downside of tucking it in out of the way is that it reduces visibility more than it would if it ran up the side of the windscreen frame.
I found there was no loss in performance after fitting the snorkle - if anything, it seemed to go a bit better.