Hey Matej,
Thanks for taking a look, I really need to talk to others that are able to print large objects like this.
The printer is enclosed, so the temperature should be uniform, aside from the temperature difference between the heated bed and the top of the printer.
I haven't tried actively heating the build chamber yet, but I wonder if I kept the entire chamber at, say 70c if it would help.
I've also tried the print with "sheath main support" enabled, and the results are the same, although the edges are definitely tidier.
Even with sheathed support, I see the same warping in long runs of support material.I suspect strongly, that if it were possible to "section" the support structures so that each run was less than 4cm or so, it would eliminate the issue.
It's currently mostly an annoyance on single extruder prints, but it's interfering with the second extruder on dual extruder prints.
Alan