The aircraft lost to corrosion at Lusaka was fairly mid-life, built 1963 for Pan Am, sold 1976 to a secondary leasing company, later to Dan-Air, lost 1977. Didn't say a lot for Pan Am's maintenance that it had degenerated, and Dan-Air were usually pretty good with older airframes - they had plenty of them.
This was something of a peak for cargo charters to Africa, consolidators like IAS had some aircraft of their own and chartered extra capacity as required. Overland transport from the African ports had degenerated due to multiple issues - railways fell into disrepair, bureaucracy by officials, handling damage, levels of theft, border difficulties, etc, and it was preferable for anything worthwhile to be airfreighted, much originating in Europe, direct to destination. Still carries on, but nowadays principally in the bellies of widebodied scheduled flights. It was always difficult finding any backload for returning freighters, and this led in part to developments such as flowers, grown in East Africa and airfreighted overnight to Europe at marginal rates.
I can't recall ever seeing a holiday flight series by Dan-Air using a 707, but did see them in brochures at the very start of Transatlantic ABC charters.