I'm running the 40vol test at the moment with very satisfactory results in my opinion. I've done a mouse and the back of a CC and it works well. Unfortunately, I'm in Britain and it's passed the point of no return weather-wise (01 October). With brief flashes of sun and even a cloudy day, this method DOES work. It's probably just worth leaving it out for two days instead of one.

P.S. I like your BL setup, uni!