a structure which is transportable in one or more sections, which— (A) in traveling mode, is 8 body feet or more in width and 40 body feet or more in length, or, when erected on site, is 320 square feet or more, (B) is built on a permanent chassis and designed to be used as a dwelling (with or without a permanent foundation when connected to required utilities) and includes plumbing, heating, and electrical heating systems, and (C) in the case of a structure manufactured after June 15, 1976, is certified as meeting the Manufactured Home Construction and Safety Standards issued under the National Manufactured Housing Construction and Safety Standards Act of 1974 ( 42 U.S.C. 5401 et seq.) by the Department of Housing and Urban Development and displays a label of such certification on the exterior of each transportable section. (c) Special rules (1) Related person For purposes of subsection (b)(1)(B), a person is related to the seller if— (A) such person bears a relationship to the seller as specified in section 267(b) or 707(b)(1), or (B) such person and the seller are engaged in trades or businesses under common control within the meanings of subsections (a) and (b) of section 52. (2) Election by both seller and buyer The credit is allowable under this section only if— (A) both the seller and the purchaser of the real property execute an affidavit representing that the sale meets the requirements of subsection (b)(1), and the purchaser acknowledges liability for the recapture of the credit under subsection (d) in case of any violation described in such subsection, (B) the purchaser of the real property records the affidavit, and (C) the affidavit is referenced in the deed to the real property. (3) Requirement The seller shall include a copy of the affidavit representing the sale with the return of tax. (d) Tax upon violation of covenant There is imposed a tax on the buyer for a violation of the covenant specified in subsection (b)(1)(C). The amount of such tax shall be 20 percent of the net proceeds after