Every insurer shall file with the department, except as to inland marine risks which by general custom of the business are not written according to manual rates or rating plans and except as to exempt commercial policies, every manual, minimum, or class rate, rating schedule or rating plan, and every other rating rule and every modification of any of these which it proposes to use. The filing exemption shall not apply to loss cost filings by advisory or rating organizations. Every filing shall state the proposed effective date and shall indicate the character and extent of coverage contemplated. Specific inland marine rates on risks specially rated, made by a rating organization, must be filed with the department.