I stumbled across this book written by French Author Joe Ceurvorst based on a trip in 1956.  I have found two different covers for it (shown below).  Most copies seem to be in the UK. The author was traveling around Africa about the same time as Dorothy and Louise.

Apparently, the writers of the Catholic Herald weren’t uber fans of the book.  Their review, in full, from March 9th, 1956, goes like this:

It may seem virtually impossible today to find real adventure, the French author of this book found it by irresponsibly taking an old liberation jeep, with a single passenger and a dog, on a round-African trip from Algiers to the Gulf of Guinea, thence to Lake Victoria, and back to Tunis via Cairo.

Our surprise, however, at his still being alive is greater than at the revelations of his story. It was worth writing, but the account is superficial. Good reading, perhaps. for a dull and oversafe train journey.

Abe Books has copies of this book

1) http://www.abebooks.co.uk/Africa-Jeep-Ceurvorst-J-Staples-1956/67949495/bd

2) http://www.abebooks.co.uk/book-search/author/ceurvorst/sortby/3/

3) http://www.abebooks.com/book-search/author/joe-ceurvorst/