Grain storage tank cover, and tanks covered

Novel covers for grain storage tanks on harvesting machines such as combines. Rigid cover panels of the cover are preferably fabricated of double-wall plastic to limit weight of the cover while providing desired strength and rigidity. The rigid cover panels can be pivoted about top edges of an underlying grain tank whereby the cover panels function as a height extension of the underlying tank, thus to increase the grain-carrying capacity of the tank. Flexible transition panels are preferably mounted to the rigid cover panels to bridge spaces between edge regions of the rigid cover panels when the rigid cover panels are raised to their upright, tank-extending orientations. A preferably single underlying actuator in the tank, in combination with mechanical linkages, can simultaneously raise all the rigid cover panels, all the flexible transition panels, and the discharge end of a clean grain elevator which discharges grain into the tank.