Paperwork for 3 border crossings
this is what we accumulated doing:
Namibia->Botswana->Zimbabwe->Zambia->Namibia. The last crossing back into Namibia produced no paper.
All the crossings were painless, bribe and hassle free, but did involved a fair bit more paperwork than a European is typically used to- nevertheless, we were treated with considerably more friendliness and courtesy than I've ever experienced, say, returning to Heathrow.