Solidworks 2004 Materials Database has the following for PVC and ABS
ABS 1020 kg/cubic meter
ABS PC 1070 kg/cubic meter
PVC Rigid 1300 kg/cubic meter
PVC 0.007 Plasticized 1290 kg/cubic meter
The ASHRAE Fundamentals Handbook (Chapter on Solar Energy) has 3 charts which plot average night sky temperature below ambient for the US. They reference the original work done in the early 1980's and observe that not much more practical work has been done in this area.