I just completed installing underbody covers on my 2019 Canadian GTI 7.5, Rabbit edition (MT, no sunroof)
First off I would like to thank all those who contributed to the enormous knowledge base compiled in this thread.
I wanted to see if I could quiet my car down. On smooth pavement it was very quiet. On tarmac with more stone contents it could get too loud to talk. Noico foam on the lower and upper trunk cover, rear footwell and under the rear seat cushion helped a bit. The car has stock suspension, intake and exhaust, and the OEM rims. Tires are Michelin Pilot Sport 3+ in summer, Nokian Hakkapeliitta R3 in WInter.
For under the engine/tranny I bought a used undertray from a DCT car. Two air openings on the driver side front, some in the rear. Made no difference (to me) in noise level, but keeps the winter salt/sand mix off engine parts and the front of the subframe.
Right behind the front subframe I installed a plastic tray with thermo insulation on the top (5Q0 825 229C). It sits under the second catalytic converter, still looking good after more than 6 months.
Further back I installed a plastic tray (5Q0 825 206K) connecting to the driver side long factory undertray and covering parts of the exhaust pipe, connecting to the fuel tank and the car floor under the rear door. No insulation on the top of that one.
Next was the Golf 8 rear axle cover (5WA 501 713), with bracket 1K0 501 682.
Lastly the two rear suspension areo covers on the lower control arms, 5Q0 501 734 and 5Q0 501 733. (for installation hardware and images please refer to earlier posts by others).
The reduction in road noise transmission was astonishing. Loving it! Glad I did this.
All the items fit as they came, no rework required.
Again, many thanks to all those who have worked on this thread and provided their knowledge.
Other covers that do not fit my car
Shooting the breeze with a buddy in Europe it became clear that the front lower control arms on my car do not fit the two different areo cover designs he was aware of (Golf 8 and Seat). One mounting hole and the opening to accommodate the height sensor bolt fit, the other mounting hole in the covers ends up being located on a sloped section of the stamping. I imagine that could maybe be dealt with using zip ties, but nah. I did not get those.
There is another Golf 8 underbody cover that goes between the passenger side long factory undertray and the fuel tank, and curving to cover between fuel tank and outer frame. The tray (5WA 825 102A) is a bit short but that could be extended easily. My buddy was surprised when he studied a photo of this underbody section of my car and saw the parking brake cable. Firstly, because he would much prefer the mechanical parking brake activation to the electronic one they have. Secondly, the cable and its support wire hanger would interfere big time with the small tray. So I did not get that one either.