I'm not getting into the debate over conductor material but would recommend Teflon for the insulator. Why? High melting temperature so less likely to damage it while soldering and then there is the whole low dielectric absorption thing.
Well the melting point seems like it should be the last reason to use teflon.
The teflon dielectric constant (k) is ~2, and I think that PVC is k=~4.0.
Cotton has a k around 1.3-1.4
K=2 is a lot lower than 4, so that is a good (and better) reason to use teflon over PVC.
like the Navy’s AEGIS cruisers. Teflon coating provides heat-protection for decades, where common PVC-coated wire will crack and degrade over time.
There is some degradation from UV, drying out, and maybe other things.
How much heat is generated in the tube equipment? The insulation only needs to insulate the wires electrically. They do not need to be insulted for heat and cold, like a wool jumper, or down jacket.
And they do not need protection from heat. The insulation is to protect them from arcing or shorting.
It is not like the amp is mission critical, or crashing over waves 24/7 in a way that requires the insulation to not chafe over time.
I would still be using the teflon before I would use consider using PVC, just not for the reason of heat protection.