Thank you! I thought as much, considering my G rosea acts the SAME way when her enclosure is too wet, so I thought the behavior looked familiar! I will add a few more vent holes, replace the old substrate with dry material and add a bottle cap for water instead of the monopoly house. Should I bother adding (literally) 1-3 drops of water on the side for humidity? Or is the bottle cap plenty for a gbb sling that size?
I would just let what you have setup dry out. It'll start moving down more as it dries out . Remember if you poke too many holes then your enclosure (and water dish) will evaporate/dry out more quickly. This will cause a lot more maintenance later with not much benefit.
Chromatopelma cyaneopubescens live in an incredibly dry environment. They build their webs among xerophilous vegetation, and their webs are used to protect themselves from the harsh climate. A bottle cap is plenty for a sling that sized, but I would add a lot more ventilation. From many keepers experiences, GBBs will not do well if there's even the slightest bit too much humidity. As long as you add more ventilation, a bottle cap is plenty of water.
GBBs can handle the dryness. I don't think the enclosure drying out is too much of a concern of the OP. Dehydration and dessication is basically non existent for this species so long as they're kept fed.
This is true, but the issue they are having isn't from lack of ventilation it's from wetting the substrate too much. My GBB enclosures has less holes then theirs does but I don't have problems as my substrate is never that wet. Once it dries out and they stop adding so much moisture to the substrate then extra holes just adds to how often you have to fill the dish. It doesn't really add much benefit to anything else at that point.