The back of the PCB(s) will get very cold, so you will need to insulate that as well. Or you'll have ice/condensation issues, and then the water will run down the card and into the PCI-e slot. And that's bad
I use two layers, the first layer is just plan closed cell insulation.
2nd layer is the black sticky back insulation, make it over sized to stop air getting in and under the first layer.
One last step, The Motherboard
You will need to insulate around the PCI-e slot with liquid electrical tape or nail polish, front and back.
Rub some vaneline or dielectric gease onto both side of the "gold fingers" that go into the PCI-e slot, and a "small" amount onto the top of the slot itself.
Also pack paper towels around the slot.
Well done, and now test your handy work.
