I wonder if it\'s just because you\'re doing 10+ laps at a time and your rotors aren\'t handling the strain of this. Becoming weakened and brittle so they crack once cooled/while cooling down. There\'s a lot of difference between doing spirited road driving and doing 200km->60km hard braking over and over again
I\'ve done ~6 trackdays, 1 with two pots, two with 4-pots and three with brembos and have never cracked a rotor, but I only do 5 laps per session generally.
Ducting as previously suggested is probably your best bet