I'm sorry, I miss read your question. If you want to put a cloth inside the cage you should make a humid hide. These work pretty well and can be made from tupperware. As for the towel on top, you pretty much leave that there all the time. I have one over my boa cage that I wet everyday and wash once a week. This has been working pretty well at keeping her humidity up.
For the lighting, BPs don't need light. They are nocturnal and don't bask. Lamps will also kill your humidity. You never want to keep a reptile cage in direct sunlight either. When you re-do your caging, get rid of the lamp and switch to an under tank heater (THIS MUST BE CONTROLLED BY AT LEAST A DIMMER, A THERMOSTAT WOULD BE BEST).