Notice of the public hearing shall be printed in the official newspaper of the Town at least five days prior to the date thereof. In addition to such published notice, the Planning Board shall cause notice to be given of the substance of every application for a special use permit, together with notice of the hearing thereon, by causing notice thereof to be mailed by certified mail, return receipt requested, or other means at least 10 days before the date of said hearing, to the owners of all property abutting that held by the applicant in the immediate area (whether or not involved in such application) and all other owners within 300 feet, or such additional distance as the Planning Board may deem advisable, from the exterior boundaries of the land involved in such application, as the names of said owners appear on the last completed assessment roll of the Town. It shall be the applicant's responsibility to issue any or all of the notices required, and proof of the mailing of such notice, in accordance with this section, must be filed by the applicant with the Planning Board. Provided that due notice has been published as above-provided and that there shall have been substantial compliance with the remaining provisions of this subsection, the failure to give notice in exact conformance herewith shall not be deemed to invalidate action taken by the Planning Board in connection with the application for a special use permit.