The board of commissioners, may, if in their judgment it seems best, issue coupon bonds not to exceed ninety-one per cent of the total amount of the taxes levied under the provisions of La. Rev. Stat. 38:1631 in denominations of not less than fifty dollars, bearing interest from their date at a rate not to exceed six per cent per annum, payable semi-annually, to mature at annual intervals within a period not exceeding forty years from and after their date commencing after a period of years not later than five years, to be determined by the board of commissioners, both principal and interest payable at some convenient banking house or trust company’s office to be named in the bonds.  The bonds shall be signed by the president of the board of commissioners, attested with the seal of the district and by the signature of the secretary of the board, and the coupons shall be signed by the facsimile signatures of the officers.  The delivery at any time thereafter of any bonds or coupons so executed shall be valid, although before the date of delivery the persons signing the bonds or coupons shall have ceased to hold office.