Slic3r dual extruder skirts and brims

I am in the process of upgrading my Hictop 3DP8 to dual extruder. The plan is to use the second extruder to print support. Does anyone know whether Slic3r treats skirts and brims as main or support material?

I'm wondering whether I need to model the skirts into my CAD model as the skirts need to be fixed firmly to the model to prevent warping.

The skirt uses all extruders, the brim is made with the perimeter-extruder.
Actually the brim is there to hold the part down. If it doesn't hold, make it wider.
The skirt has a different meaning. Priming both nozzles and acting as wipe and prime tower, when more than one skirt-layer is defined. Also it keeps the air inside the skirt calm and warm.

Thank you. My mistake, the skirt was irrelevant, though I will now look into using one after you pointed out its usefulness.

I presume the perimeter extruder means the extruder that prints support material? If so, does it function correctly and prevent warping, if it is wide enough?

Anyway, from what you tell me I do not need to model a skirt, just let Slic3r apply it.

Sorry, I don't understand the third sentence, regarding wipe and prime tower.