Phenethylamines are usually pretty stable, so I wouldnt worry about leaving it in the car. As for shelf clife, if kept in the right conditions itll last a looooooooooong time.
To be safe, get yourself an amber vial, stick it in there along with a desiccant, and stick that in a dark and cool place. If you want to be extra careful, stick it in the fridge, but make sure its in a dry place where no moisture would get in.
Ive had 2C-B in just my normal stash safe for months upon months with absolutely no qualms whatsoever.
Keep it away from moisture
Try to keep it away from unnecessary heat
Try to keep it out of the light
You should be golden mate!