Marine and transportation insurance policy premiums on trip risks not terminated shall be deemed unearned. The commissioner may require the insurer to carry a reserve equal to one hundred per cent on trip risks written during the month ended as of the date of statement, and:
(1) Computed upon a pro rata basis; or
(2) With the commissioner's consent, in accordance with the alternative methods provided in section 431:5-301(c) and section 431:5-301(d).