Well, I bit the bullet yesterday and moved the chids into my little greenhouse.
For the past week I've been monitoring temps and humidity using my idea of borrowing the heat from my workshop to warm the ghouse. Well, half of my idea worked, the other half didn't.
Temperature wasn't too hard to control but I found I had no control over humidity. I could soak the greenhouse floor and benches with water and the humidity jumped to about 40% and then within half an hour it fell back to about 30%. My shop was supplying heat but stealing all the humidity.
This morning I went to Lowes and got a DeLonghi space heater. With the heater on and the doors to my shop closed things started to look much better. I added a small 4 inch muffin fan to help move the heat around. Tonight I think I might be able to grow orchids instead of cactus.
I just checked the ghouse tonight it's 25f outside and temps are right around 60F and the humidity is right at 50%, instead of 25% like last night.
Pictures of my puny collection.