To have a high rate of success with seed propagation, it's a good idea to use heating mats so you can maintain a constant temperature. I use heating mats with a thermostat for all of my seeds, and generally maintain a temperature of about 80F. The seeds go in a propagation tray with a dome to keep in heat and moisture. With this setup, you can propagate seeds at any time of the year without the expense of keeping the whole greenhouse heated.

I usually plant my seeds in my house so I can keep an eye on my "babies"! Once they get going, I thin them out and move to the greenhouse.

I've had the best success with seeds germinating them in my sunroom and moving them to the GHs soon afterward. I keep the heat set at 60F. Less than that and the warmth lovers don't do well. Those are the eggplants, peppers and tomatoes.

I've found that my seedlings like the same environment as I do. I start them in the house and then move them to the GH once established. That way I don't have to burn electricity. Heck I have to heat the house, might as well take advantage of it.
Dave