I think I know what you’re thinking: why is he fitting a carpet?!
The reason is actually quite simple; the tunnel sides can get really hot and even that thin bit of carpet takes the edge of that heat, especially noticeable during the summer. The other reason is that it’s standard 420R spec.
I prepared the carpets a couple of days before actually fitting them by laying them flat, because they are supplied tightly rolled up in a packet.
The heat can be a problem for some spray glues I’ve tried in the past. I had the best results with 3M 08080 spray adhesive, which seems to stand up well to the tunnel heat. What tends to happen is the front edge (closest to the engine) comes unglued and you end up re-doing part of this job every so often, but with restricted access.
I masked the area before spraying glue. Using masking paper is a little over the top, but the masking tape keeps things neat and you can always clean off overspray with a good glue remover (like Auto Glym Tar and Adhesive Remover). Remember the carpet doesn’t extent all the way into the pedal box so be careful to mask the correct area.
I sprayed the glue on both the tunnel side and the carpet back and waited for the glue to become tacky. To locate the carpet, I used the chassis rail mid way down the tunnel first, then the seatbelt mounting hole at the back of the tunnel. With those to points located, the rest of the carpet can be pressed on the tunnel, and it will be in the correct location. This is where it is not helpful to have a carpet tries to roll itself back up again.
I normally add a little more adhesive to the front edge (because of the heat), but on the left-hand side there is the access bung for the 5-speed Mazda gearbox oil fill plug. So this time I kept the glue lighter in this area, because the carpet will have to be peeled back in this area at some stage. There is also an access bung on the right-hand side, which is for the 6-speed-gearbox reverse-light switch, so I had no need to reduce the glue in this area.