Kurtje, that's one cool looking track.
You could also try running short wheelbase and/or the 1 degree rear hubs that will then give 4 degrees of rear toe in, a ball diff may also help. Tom Cockerill has posted a set up on PetitRC for low grip conditions, perhaps some of this set up could help and give you some pointers. You can find it here;
http://www.petitrc.com/setup/schumac...ill_RHR201312/