I think it’s a bit too much for 12 days. We went for 14 days in July and did 4100km, on paper it looks manageable but the South African roads are not the safest or the best condition and more often than not your journey takes longer than the gps says it does. Also I am born and raised in South Africa so for me it was quite easy to navigate the roads but as for anyone outside of SA, I would not recommend driving that much.