Let the sub dry out and leave it bone dry. A waterdish is all they need. Having damp sub can create a stuffy enclosure and that's the common cause of an avics deathCouple of pics of the avic sling.
Keep finding him halfway down the container.
Don't think he can decide wether he is an arboreal or just a thirsty spider!.
I keep the substrate moist and a full water dish.