Section 20B. No salvage title need be obtained for: (1) a vehicle owned by the United States unless it is registered in accordance with the provisions of chapter ninety; (2) a vehicle moved solely by animal power; (3) an implement of husbandry; (4) special mobile equipment; (5) trailers; (6) passenger vehicles ten or more years old; or (7) manufactured homes as defined in section thirty-two Q of chapter one hundred and forty.