The phrase 'little white van' isn't used as part of the characters' dialogue, though, Songs - it's the narrative. McCall doesn't go on and on about other features in the books (and I've read four or five of them by now), and his writing otherwise is pretty straightforward. There's nothing wrong with the conversations, they seem pretty authentic, just the literary tic of the little white van.
The Little White Van (to the tune of The Little White Bull)
There once was a van, a little white van
Chorus: (little white van)
Driven by a lady and not by a man
Chorus: (little white van)
And when it was good
It went how it should,
But when it broke down
Miles out of the town
Mama Ramotswe took a petrol can
Chorus: (a petrol can)
To that little white van
Chorus: (little white van)
And sprinkled the petrol and quickly ran
Chorus: (and quickly ran)
And that was the end of the little white van
Chorus: (the little white van)
And the people stood
And threw on some wood
They clapped and cheered
And some of them jeered
And that was the end of the little white van
Chorus: (thank f*ck for that,
It won't be back, the little white van...)