The vapor barrier idea can be useful for this. It is described well by Jack Stephenson; you can probably find it by googling "Warmlite, vapor barriers, Jack Stephenson."
Layering and vapor barriers, good insulation from cold ground -- I don't see why you couldn't do it all without the expensive ready-made stuff.
In moderate temperatures, it wouldn't be too difficult to make this approach work.
If it is too warm, vapor barriers can be uncomfortable; but partial vapor barriers can still be useful (materials such as thin, uncoated nylon windbreaker fabrics that slow the movement of water vapor, but do not block it entirely).