Things that turned out to work
PEEK instead of PTFE for the thermal insualtor
PTFE is just to soft. PEEK has too disadvantages: it has more friction so its harder to unscrew the M6 winding which was once a problem because the heating barrel broke when we headcrashed into the base. Because we could not get a grip on the broken part we could not unscrew it. but a PTFE part would have bent and would also be destroyed. Next thing i want to try out is a PEEK PTFE mix so it should have better friction. The other problem is cost. It costs about 200euro per kg. we got a 20mmx30cm zylinder for 60euros. We only lost on PEEK part so far. We destroyed about 8 PTFE parts in accidents before.
Acrylic base plate
a milled acrylic base plate provides good sticking for ABS.
Heated base plate
If you can heat the object, the internal stresses that normally build up while each layer cools off seperatly gets reduced and so you can make relly flat objects. We have not tried out adrians fan solution but that might be an even simpler solution. That would also be easier to use with the acrylic base plate that provides better sticking than the heated copper plate.