The Secretary of Agriculture, under such regulations as he may prescribe and at rates and for periods not exceeding thirty years as determined by him, is authorized to permit the use by public and private agencies, corporations, firms, associations, or individuals, of structures or improvements under the administrative control of the Forest Service and land used in connection therewith: , That as all or a part of the consideration for permits issued under this section, the Secretary may require the permittees at their expense to renovate, recondition, improve, and maintain the structures and land to a satisfactory standard.Provided