painting the wood shouldn't be a problem as long as its dry before he's in there. I actually went to home depot and bought sheets of flexible plexiglass (looks like white cardboard) and used that with some water proof silicone to seal the bottom and protect the wood. The rest never has that much water contact so I don't worry about it. I did spray the plexiglass with some spray paint though and it hasn't caused any problems. Like I said, make sure it's dry and won't chip off.
Edit:
I would recommend a larger enclosure. 4x2x4 is perfect for the panther by himself. Half of that is too small IMO.