Yes that method gets used a lot also and usually has better results then the space sheet.
The biggest point to keep in mind is that most materials that you could use to insulate under your body lose most of the insulation qualities by being compressed under your body. For best results you want to create a static air zone under your body so that convection and air-movement don't rob you of body heat.
I ride a recumbent.
I like to HAM it up on the CW.
I use Linux.
I play go.
Of course I sleep in a hammock!