Have a look at the newer Garmin Oregon range , most garmin "outdoor" GPS's have a worldwide basemap included which is pretty useless.
The Oregon is complete touch-screen and water/shock proof and has served me well so far.
(issues regarding average back-light performance has not affected me)
You will have to load the Africa Topographic maps separately (bought from your local camping store or online) , the above model can take street and topo maps simultaneously so can serve in Automotive mode/ Geocaching/ hiking etc..
They have 850MB onboard memory, you can extend this by adding a mini SD card.
Don't forget the legendary GPSMAP 60CSx model - its also a safe choice if you can still get one as these are previous generation.
Cheers