I saw a few bits here and elsewhere on it, but I have yet to find something that explains its usage, in detail(e.g. in positive and negative contexts and in different tenses). Anyone know?
It only means "either way", "anyhow", "anyway", etc with a fatalist nuance, hence it can sound negative for some.
You can find it as other forms like どっちにしろ or どっちにせよ.
While I'm sure the underlying grammar makes the analogy a rather liberal one, I have always tended to feel that these were similar to patters in English that use "be". That is, an old form of the subjunctive:
Be it A, or be it B, it's fine regardless.
Whichever it be.
Whatever the case be.
The pattern can always (well, usually) be reworded using も to mean essentially the same thing.
なんせ* (no strict conversion; maybe 何が何でも)
Since it is late to go now, I decided not go anyway.
It is similar to "anyway". But, you should use "douse" in negative context only.