Not as silly as it sounds. As alluded above, Qantas' early 747s were fitted with what was called a Lower Lobe Galley, complete with a lift from the main deck to the galley underneath.
For cabin crew rest on what were then long-range sectors (BKK/LHR, BKK/FRA and,I think, AKL/LAX and vv), B747-300 aircraft were fitted with a fully furnished and equipped container on the lower deck. Access was via a man-hole and ladder in one of the galleys. The container was fitted with quite a few bunks that allowed complete horizontal rest and maybe even dancing. It was acceptable to both the regulator and cabin crew unions.
With imaginative thinking anything is possible especially if freight is limited due to payload restrictions. Bear in mind that a pallet of freight could equal as much as 45 pax, depending on the notional weight of the pax and baggage.