The Directors of the Corporation who are employed in the Department shall receive no additional compensation for their services as such Directors but may be allowed necessary traveling and subsistence expenses when engaged in business of the Corporation, outside of the District of Columbia. The Directors of the Corporation who are not employed by the Federal Government shall be paid such compensation for their services as Directors as the Secretary shall determine, but such compensation shall not exceed the daily equivalent of the rate prescribed for grade GS–18 under section
5332 of title
5 when actually employed, and actual necessary traveling and subsistence expenses, or a per diem allowance in lieu of subsistence expenses, as authorized by section
5703 of title
5 for persons in Government service employed intermittently, when on the business of the Corporation away from their homes or regular places of business.