I like the foil bag.
I once had two Fords in my driveway. I only wanted one key. Rather than messing with lock cylinders and such I had a hardware store cut me a key - one side was cut to one car and the other side to the other car. It just meant that it mattered which way I put the key in.
Anyway - I know that your situation is completely different. But I’m wondering whether you’ve asked at the dealer whether or not they can reprogram the vehicles to use the same FOB. One FOB that works on either car. I don’t know these systems well, so that could cause other problems. But it’s just a thought.