frig left on

I leave mine off, open and unloaded between trips. It gets HOT here and once the outside air is above 90 or so, the little fridge can't keep it's interior cool enough during those warm hours to keep food safe for weeks. Plus consider if there is ever a breaker trip or other power issue, you aren't checking daily and could really end up with a stinking mess if something went wrong. My unit uses 300 watts per hour averaged over a 24 hour day, so call it $1.30 a day to run.
I'll power up the fridge the night before to cool it down, then load it up just prior to leaving.