I have a red heeler and a kelpie (35 and 40 lbs). I used a 6ft long double layer of reflectex on the ground with a fleece sleeping bag on top. I open it up, get them to lay down on the bottom part, and then, once they are settled, partially cover them up with the top part. That worked pretty well until it got down to around 50 degrees. Then, I added a cheap 20 degree kid sleeping bag from WM. It got down to 40 and they were nice and cozy warm.

The problem with short haired dogs is that they will get cold faster than you do since they have a lot less body mass. So, they need more insulation than you do. Because of that, it's pretty difficult to carry enough insulation for them when you're hiking.

If I'm car camping, I don't take them if it's going to be colder than 40 degrees. If I'm hiking, I probably wouldn't take them unless I knew it wasn't going to drop below 60 at night or I was willing to carry that 20 degree kid sleeping bag for them.

One thing I recommend is doing some test overnighters to see what temperature your dogs are comfortable with at night. If they are curled up into a tight ball, even if they are not shivering, it's pretty uncomfortable for them. Be kind and make sure they are warm and comfortable when you camp.