I would say to keep it around 40%. Anybody plz correct me if I'm wrong but thts what I keep my Greeks at and Russians have about the same care requirements
Usually when we talk about humidity, moisture, etc. we USUALLY are talking about leopards and sulcatas. The mediterranean species do not require as much humidity to grow smoothly. And when we talk about a humid environment, it is USUALLY for your BABY tortoise. Once they get to be a bit bigger, say over a year, its not as important.
If you have a baby russian, the most healthful thing you can do for it is provide good UVB and calcium, and feed it properly. If your russian is an older tortoise, keeping it a semi-dry environment would be just fine, with weekly soaks or a in house waterer. Here's what Joe Heinen of the russiantortoise.org says about keeping your adult russian tortoise:
"Rubbermaid storage containers: These are an inexpensive indoor pen. The 50 gallon container is an ideal starting point for one tortoise. They are light and easy to clean. They are opaque so the animal can't see out. The best part is....they only cost $15 ! Keep in mind that bigger is better. I use this as a temporary set up for when I have to keep one inside. IMPORTANT: this setup keeps the humidity at around 60%. As the substrate dries out it is critical to add water. Don't let it get dry and dusty !!! Sand alone makes a very poor substrate."