In reply to ffati:
I used black-out lining (white) and net curtain wires from the local haberdashers for the summer curtains, but the wires sag in the middle and let in the light so strongly recommend curtain rails. The black out lining is good though. Easy to cut, no need to hem and the white reflects the light so the van is nice and light with the curtain is closed - also despite the sag the van is still darker than a tent in the morning. If going the velcro route make sure you get decent quality velcro that will last. I have some cheaper velcro that has lost its grip as curtain ties (double sided).
I insulated the van with 10mm Polyethylene (PE) carpet underlay (NOT PU Polyurethane sponge!) from which I made insulated window panels. Its the same stuff that carry mats are made of and pretty cheep. Easy to mark and cut. I ordered 50m from a carpet wholesaler (the local carpet shops don't do it) where about 30m would have done, but now have a 20mm insulating layer and these nice winter window covers. The flexible nature of the PE means that when cut accurately they just sit in the windows without any attachments.