Hello Daydreaming,
I have 2 cousins of your frog, kassina senegalensis. Mine are quite shy too, I house them in a 2 and half foot tank which I divided into two halves with a piece of plastic siliconed into place. Half is dry compost, half is part boggy compost part water.
One thing I will say is that they like to hide, I have some PVC pipe buried in the substrate (with the ends open) and this is where they spend the majority of the time. I also made a little cave by digging a dip in the compost and placing a piece of slate on top, this is another favourite hiding spot.
Make sure any water area is easy to get out of, don't know if it's just my two, but they seem a little lacking in the brains department and will try for ages to climb out a slope that's too steep! I've solved this by making a gentle ramp from gravel so they find their way out, bless them! Obviously if it's a water bowl you have just make sure they can reach the lip of it easily. Would love to see photos of your frogs, I have some photos of my set-up on the forum here somewhere, I think in the introductions.