The salinity seems pretty stable. I top up the tank with distilled water a couple times a week. I'm sure the temperature fluctuates a bit. I pulled out the floating thermometer a couple weeks ago, and a digital thermometer is in the mail (with the skimmer).
I found that with most of my tanks, the temperature usually stays pretty stable in the winter when the room temperature is less than the tank temperature. In the summer, unless the A/C is on, my tanks tend to heat up quite a bit. I can't really do much about that, so I stopped worrying about it a couple summers ago.