The present invention is predicated upon methods and devices for positively mounting structural members while preventing or substantially limiting exposure of such members to environmental conditions possibly leading to corrosion. Static reference points are ascertained by measuring field strengths of the WLAN stations at spatial coordinates, aided by WLAN client, and assignment of the measured field strengths to the spatial coordinates in terms of data records. The air chambers can be formed for instance by creating recesses in the relevant layer from the top, or by removing material from the layer at different location after arranging thereof, for instance by melting or biological decomposition of inclusions.