Under the Institution Bond Act, any escrowed proceeds may be invested or reinvested in bonds or notes of the United States or any of its agencies or instrumentalities, or in bonds or notes where the principal and interest is unconditionally guaranteed by the United States. The escrowed proceeds and investments, together with any interest to be derived from the investments, shall always be sufficient for payment of the bonds, refunded as they become due at their respective maturities, or at prior-redemption dates, including the principal, any prior-redemption premium and any escrow agent charges.