I think it depends on what type of insurance (and I don't think the instructions provide guidance, at least not clear guidance).
If term, and yes, I have seen plans with term insurance, then it is definitely an expense item...I'd use line 8g (SF) "Other."
If whole life or UL or some variant that develops a cash value, then I treat it as any other asset of the plan, so premiums are really transfers and don't get reported anywhere. The gains or losses are part of the "other income" on 8b (again, the SF form).