So I'm setting up an enclosure for a Colombian Red Tail Boa I'm getting in a couple weeks and I've almost got it perfect. I have it well-decorated with fake plants, some hides, rocks and branches, and it would be ready if it weren't for the fact that I can't get the humidity to stay above 50%. The enclosure has a really big water bowl and I'm using Zoo Med Eco Earth for the substrate. Is there another kind of substrate that is better at keeping high humidity? I'm considering possibly adding some live plants to the terrarium. Are there any easy to take care of plants that would be good for raising the humidity?

Note: this is a melamine enclosure that I made, so it doesn't have a screen top where the humidity could escape easily.

Thanks for any helpful advice you have to offer!