Any person desiring to erect or increase the height of any structure, or to permit the growth of any tree, or otherwise use his property in violation of airport zoning regulations adopted under sections 67.1200 to 67.1222, may apply to the board of adjustment for a variance from the zoning regulations. Such variances shall be allowed where a literal application or enforcement of the regulations would result in practical difficulty or unnecessary hardship and the relief granted would not be contrary to the public interest, except that any such variance may be allowed subject to any reasonable conditions that the board of adjustment may deem necessary to effectuate the purposes of sections 67.1200 to 67.1222, including the reservation of the right of the municipality, at its own expense, to install, operate, and maintain thereon such markers and lights as may be necessary to indicate to operators of military aircraft the presence of the airport hazard.