gently downwards – without resting it on the ladders, or it will get dented or buckled.

As the collector arrives fully at roof level, it should be laid flat and secured (roof jacks and a plank will do this, even on a steep roof). The two ladder-climbers can then get onto the roof (securing themselves with appropriate safety gear) and help carry the collector carefully to its final installation spot, where it can be fixed into place.