GST credit in insurance premium

ITC on inward supply is available subject to section 16 except supply is blocked u/s 17(5).
As ITC credit on stock insurance is not considered as blocked u/s 17(5), you can claim ITC for same.

GST paid on insurance is not your expenses, because ITC is available for same.
So, only basic amount (excluding GST) is your expenses, so you have to calculate prepaid expenses on basis of basic amount only.

What if it is the case of vehicle insurance

FOR vehicles, if Goods carriage Vehicle that you can take ITC on insurance for that.