Turn it on a day before on gas. Make sure your battery(s) have a full charge however. The fridge will shut off if it doesn't have enough juice. In case you are not sure of anything regarding your RV'ing needs. RV.net is a fountain of knowledge. There are platny of opinions there also, take it with a grain of salt.
Your fridge doesn't circulate cold air, it is a gas-absorbtion system. it SLOWLY sucks the heat out of the products inside it. This is why you need to put cold item in for best results. I use the tub for the beer when it is me and the guys. We put in all the beer we can fit, and Ice it down. Ofcourse I have a motorhome, and we have access the whole time. LOL