Except as hereinafter provided, an owner shall not demand, accept, or retain rent for a mobile home space exceeding the rent in effect for said space on the effective date of the ordinance codified in this chapter. If a previously rented mobile home space was not rented on the effective date of the ordinance codified in this chapter, the owner shall not, except as hereinafter provided, demand, accept or retain rent for said space exceeding the rent in effect during the last month the space was rented prior to the effective date of the ordinance codified in this chapter.