(1) Any person, firm, or corporation engaged in the manufacture or processing of personal property in this state which property is stored in a public or private warehouse structure or area must file a full declaration of such property as of the assessment date with the county assessor. On any assessment made on personal property manufactured or processed in this state by person [persons], firms or corporations having a domicile or place of business in Idaho, being stored in a public or private warehouse structure or area, the board of equalization of the county in which such assessment was made, at its meeting on the first Monday of December as provided by law for equalizing the assessments of personal property on the subsequent personal property assessment roll, shall cancel such assessments in whole or proportionate part on receipt of sufficient documentary proof that the personal property so assessed was actually sold and transported or shipped to another point outside the state of Idaho on or before December 1 of the current year of assessment. No such cancellation shall be made unless such proof be furnished to said board on or before such meeting in such year. The term "manufactured" or "processed" as used herein refers to personal property which has been fabricated, constructed, assembled, milled or converted into a finished product and is not intended to include any personal property undergoing a stage of manufacture or process prior to the end finished product.