Both the bottled gases (propane/butane) used in the leisure sector and the substances used in narcotic gas attacks are heavier in gaseous form than air, meaning that they initially collect at the bottom of the vehicle.
A corresponding gas sensor should therefore always be mounted below the sleeping areas in/on a vertical surface. About 10–30 cm above the floor is the right height. In this way, you will have enough time to react in an emergency.
If the space is divided by curtains or sliding doors, a further gas sensor or standalone gas alarm makes sense.
Please ensure a sufficient distance from the sensor to heating outlets and gassing batteries in each case.
In contrast, CO sensors are preferably mounted as high as possible. Close to the ceiling is optimal.