I'm a noob here but I'm learned a few tricks to building a coolerdor.

Bleach is perfectly safe for your cooler and it kills nasties at as low as a few ppm. I used it for year to sanitize my beer and wine bottles prior to bottling for that reason. If you use like 1 tbsp per gallon of water and triple rinse you will have no bleach residue or smell. Let the cooler air dry and keep it open until the plastic smell is gone. 2-5 days unless you get some really stinky plastic. Realistically though, if you get some cedar to line the walls then the plastic smell will not even be an issue. My cooler actually smells more cedary than my humidors do.