First - be really careful about the ribbon cable. This is usually one of the main points of failure on the boards. If you don't have to remove it, don't.
You are right to want to insulate the board. One option is to put it inside a plastic bag but I'm not certain how much heat is generated by one. You might want to bench test that idea and keep a close monitor of the temperature inside the bag with a thermometer. If it gets very hot, turn it off.
If possible, construct a small plastic box to put the card inside and drill holes in it for ventilation.
Can you somehow mount the card firmly inside the dash? If so, you can bolt it in and make sure nothing that can short it will touch the card.