I would definitely prepare for colder than expected. as pointed out, better to have it and not need it, than to need it and not have it. not only might he not want to go again, his mother probably wouldn't ever forgive you.

Honestly, considering that, I would take a rain check or go someplace within your experience and stick with conditions that you're confident of for introducing him to this sort of thing.

It's one thing to take the risk for yourself, entirely different to risk somebody else. It'd be different if he knew what he was getting into, but you're the experienced one, and you're not even sure what you're getting into.

if you're both experienced in survival methods, and you have confidence that he can get through it without you if you get separated, then ok.

I have a 0°F (+5oz) UGQ quilt set, and woke up this morning to -5°F. I was wearing a heavy thermal base layer, and though I was warm, i could feel the outside cold through the quilt. Pretty sure I've been to -13°F with this setup, but I'm wondering now if I'm mis-remembering +13°F... either way, I have backup in the form of my summer quilt set, a reactor liner, and a full body length 36"wide reflectix... which is good, because -12°F low is in the forecast.

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