Fully executed duplicates of bonds, trust fund agreements, and trust agreements maintained under the regulations in this part, and fully executed duplicates of all endorsements, amendments, riders, indemnity agreements, and other attachments thereto, and photographically reproduced copies of any letter of credit or amendment thereto, shall be filed with the Regional Director for the region in which the registrant, packer, or person applying for registration resides, or in the case of a corporation, where the corporation has its home office: Provided, that if such registrant, packer, or person does not engage in business in such area, the foregoing documents shall be filed with the Regional Director for the region in which the place of business of the registrant or packer or person is located.