A low-pressure mercury vapor discharge lamp has a discharge vessel enclosing, in a gastight manner, a discharge space provided with a filling of mercury and a rare gas. At least one opening is formed on each of the planar portions. The vehicles also have a second air conditioning system adapted to condition at least air in the sleeper compartment. An outer circumference of the annular groove is less than an outer circumference of the circumferential support. According to the invention, one of the lateral edges of the base comprises a rib which corresponds to a longitudinal recess on the inner part of one of the sides of the guide, while the other side of the base comprises a crimp which can be engaged with an inner step on the other side of the guide. The continuous interconnecting void is configured to receive pourable concrete which creates a support structure for the plurality of GRC forms when the concrete hardens and to permanently join the plurality of GRC forms together.