From personal experience I'd suggest a glass terrarium of around 45x45x60 cm (width x depth x height) for an adult or pair.
I use a mix of orchid bark/Eco earth (coco husk) as substrate and keep
moisture at between 60/80 percent by spraying once in the evening.
Temps in winter can drop to low 60s F and in summer try to keep below high 80's, they don't like extreme heat. Provide lots of climbing and cover, I use cork
bark and tubes plus half plant pots. Also a few fake ivy style plants
to drape around the setup.
I also feed dubia roaches (small/medium) in bowls to stop them burrowing and hiding in the substrate. The cavies now wait by the bowls when it's writing towards feeding time (as it gets dark).
That's about it really, cover/climbing/moisture I find are the key to keeping them happy!
I don't have that problem in Wisconsin and use central air so that is likely why. I have more of a problem keeping temp and humidity up in winter, have to mist (or should I say soak) the cage twice daily. I would place a fan blowing towards aquarium. I also use sphagnum moss since I like how it holds moisture. Just noticed how old this post is but this is what I do anyways .