A method of securing a double-wall panel having a plurality of hollow chambers to a substructure of a greenhouse or the like, which has a number of crossing rods. A number of clamping devices spaced from each other are mounted on the transversal rods of the substructure. Each clamping device includes a hooked anchor inserted into the wall of the panel and a U-shaped clamp connected to the anchor and placed over the transversal rod. One clamping device is positioned on the rod in the center of the lower wall of the panel and is secured to that wall to produce a central anchorage, which is immovable in all directions. Two lateral clamping devices are positioned on the same rod at each side from the central clamping device. The U-shaped clamps of the lateral clamping devices are placed over the rod with play.