I would just stick to a healthy diet, adding just a pinch of calcium every other day or so. To much can be really bad for their kidneys.
Good UVB light is a must too.
I wouldnt put anything with wires inside the box. She will rip it to shreds. The video I linked shows how much digging they do and it can go on for days. The box in the vid is bigger then it looks and it wasnt even ready yet when she started at it lol
I have always used the big plastic totes with no problems using the under tank mats.
You could also place over a heat vent ,ad a little water each day. As long as your vents set to about 70 to 75 .the humidity will make the box feel warmer to her if you keep the lid on.