Or... go buy a new acurite or hygrometer. They are so variable anyways... I can't believe that it's anywhere below 50% in your set up like that, it looks to have very minimal air holes, so it can't really be very low.

Like the VPI book says, they can and will seek out higher humidity by going under the newspaper, and newspaper likes to suck up water vapor, so the snakes will have higher humidity under the paper and in their hide as well.

The best you can really do is try and possibly find an accurate hygrometer (yes, another 12$ gone!) or if they shed perfect, assume that the humidity level you are providing is ample for that snake.