first chicane: I'm braking ever so slightly on turn-in, smashing the first apex, then turning back sharply, sometimes putting both front wheels on the grass and sliding the back end on the road.
uphill left: I'm braking early from as far as possible to the right, then getting some slight drift on turn in, then understeering out of that, hitting a late apex, and (hopefully) not having to turn way from the wall on the right.
tunnel turn: No idea....I think you have to take the late apex again and use as much of the concrete stuff that is allowed.
And yes, I just did some laps, and if you get the line right, from out of the tunnel is it completely flat, the hardest apart is hitting that apex on the second last corner that is blind behind the crest, I myself put two wheel on the grass on that bit.
Note: I'm using the bathurst