Hand helds have to be 10BC per the GCR. They do not expire.
Hand helds don't expire, but they do get old. If they sit too long the chemical can kind of cake up. I've seen guys doing inspections on them (in industrial settings where they are requried to inspect every so often) will turn them upside down & shake them.

I think you will find that a marine application has a better mount for your car than what you'll find at HD.

FWIW I'd mount it to the floor just because its lower.