^Thanks for that Polyglot.
Water has an impressively high heat capacity, so it takes quite a bit of energy to get up to temperature and it's hard to say if your little heater is up to the task. But I'll assume you're not starting with cold water, so it could very well work
Toad, being an aliphatic hydrocarbon, butane is fairly unreactive to most chemicals---but highly flammable! It should be fine for keeping oxygen out of your chemistry, as long as you're spraying it in a well ventilated area. Nitrogen, helium, and argon are also potential options, and possibly better options, if you have access to them.
After each use I pour my chemicals back to their stock bottles so they are replenished. If you do it this way the volume of your stock will be constant and you can buy bottles to fit the volumes snugly.