An upper cabinet of a rotary-drum laundry dryer outer casing can include a rear wall. The rear wall can include a sink-shaped bulge or recess. The bulge or recess can project outwards of the upper cabinet, be roughly centered to a rear rim of a dryer drum, and include a through opening. The upper cabinet can also include a substantially circular, basin-shaped lid or cover fixed to the inner face of the cabinet rear wall substantially coaxial to the drum. The lid or cover can be shaped so as to completely cover and close the outwards-projecting bulge or recess on the cabinet rear wall. This can form, on that rear wall, a cavity which communicates with the inside of drum and also with a hot-air generator via the through opening.