Hi,
I thought I would share how I keep and display my scorpions. The same setup could be used for tarantulas. The way it has been setup is to allow independent control of each enclosure. So you can have a moist tropical enclosure right next to a bone dry enclosure, as you will see in the following pictures.
I hope it helps
The first picture is of the units and enclosures I use. Each unit holds 6 large enclosures and multiple smaller ones.
The unit has heating pads and lights fitted to it.