Litz versus aluminium tube
I've seen photos of MegaWatt electric furnaces (steel processing) fed the 60Hz power with 40 cables, each 2inch diameter and of flexible wired, arranged in 3 foot ring. In retrospect, the spacings were respecting the 8mm skindepth at 60Hz.

What caught my eye was the 3 foot ring of support, to hold the cables apart, either for heat removal! or for skin-depth minimization.