The bonds must be issued as serial bonds, maturing in equal or unequal amounts, at those times and on those occasions, and in denominations as the trustees determine. However, the last maturing bonds of any issue must be expressed to mature not later than twenty years from their date, and the first maturing bonds of any issue must fall due not later than five years from their date. The bonds shall bear a rate of interest, payable on occasions as the trustees prescribe, and must be payable in a medium of payment and at a place as the resolutions prescribe. Bonds may be issued with provisions permitting their redemption before their stated maturity, at a time and under conditions as the trustees prescribe. Bonds made subject to redemption before their stated maturities may contain a provision requiring the payment of a premium for the privilege of exercising the right of redemption, in an amount the trustees prescribe. All bonds that are subject to redemption must contain a statement to that effect on the face or reverse of each bond. A resolution authorizing redeemable bonds must contain provisions specifying the manner of call and the notice that must be given.