The provisions of this section shall apply to all insurance which is now or hereafter defined by statute, by ruling of the commissioner or by lawful custom as inland marine insurance, but this article shall not apply to insurance of vessels or craft, their cargoes, marine builder's risks, marine protection and indemnity, or other risks commonly insured under marine insurance policies:

(1) As to all classes of inland marine insurance for which class rates or rating plans are customarily fixed by rating organizations or associations of underwriters, rates or rating plans shall be filed by all authorized insurers writing such classes, with the department in such manner and form as it shall direct, and also special rates fixed by any such rating organization or association shall be similarly filed. All such rates shall be reasonable, adequate and not unfairly discriminatory. Due consideration shall be given to past experience within the state and outside the state when necessary, and due consideration may be given to prospective loss experience within the state and without when necessary, including catastrophe hazards, to a reasonable margin for profit and contingencies, to policyholders' dividends in the case of participating insurers and to all other relevant factors within the state and without the state when necessary;

(2) Any filing made pursuant to this section shall be approved by the commissioner unless he finds that such filing does not meet the requirements of this section. As soon as reasonably possible after the filing has been made, the commissioner shall in writing approve or disapprove the same; provided, however, that any filing of class rates, special rates, or rating plans shall be deemed approved unless disapproved within 30 days. The commissioner may investigate rates not required to be filed under the provisions of this section and may require the filing of any particular rate not otherwise required to be filed; and

(3) An insurer may satisfy its obligation to make such filings by becoming a member of, or a subscriber to, a licensed rating organization which makes such filings and by authorizing the department to accept such filings on its behalf. An insurer may belong or subscribe to an inland marine rating organization for inland marine insurance and also to other rating organizations for other types of insurance.