Yeah, we have to heat our "room" up a good hour before hand to attempt any tuning at all. John, we use 200/side @ 8ohms, our Crown doesn't get too hot at all. Soon we'll be running 375, I hope you're right...
Kerosene is good and bad. It smells like shit and you'll need to move it IMMEDIATELY after you extinguish the flame. But it uses no electricity and it's very portable.
Insulation? Helps, but don't count on your room staying "right" for over twelve hours. That is, if you practice twice a week, like we do, you'll need to remember to heat up early (electric is fine for this, maybe 3 hours beforehand) and if it's an independent structure, you'll probably want an auto-heater. Ours features "FreezeGuard," something that's supposed to keep our room from ever freezing.
I'm undecided on the humidity deal. Our heater also features a humidifier, which can help to make the room seem warmer. I'm tempted to say, "Look, cut that out," but you see them in serious studios on occasion (the humidifier, that is). We also have a DEhumidifier, so after practice, that gets turned on.
Wax On Wax Off. Anybody?