"Is it better to leave the frig on all the time or turn it off when stored?"
I really think it does not matter which way you do it. It's really all about how convenient you want the refrigerator for your use.
We also plug in at home, 24x7x365 and the refrigerator is on all the time.
We use the camper all year round too, when not camping, in the driveway. We sleep in it almost every night. Our house is really just a spot to plug the camper in! Really.... the house is a convenience for the camper! That's why we chose this place.
We keep food items and drinks in the camper, pretty much, all year round. Except in the coldest of the months, when temperatures reach zero or below, and we're not heating the camper.
Does it hurt anything to leave them on 24x7x356? No. Does it hurt anything to turn them off 24x7x356? No.
But if you use your camper a lot, it's much easier to just leave the refrigerator turned on and keep it cool, rather than trying to cool it every other day.
I have no clue what the electric usage is on the refrigerator. I really don't care. When we hang out in the camper, we're not air conditioning the house. The cost of cooling the refrigerator, and even running the air conditioner for a box that's 380 square feet is definitely cheaper on the electric bill than attempting to air condition a 2800 square foot box!
Either way, on or off, it's your choice. How much do you want to use it? FYI, the RV refrigerator is a great over-flow and a secondary refrigerator option for your house too! Works great. We keep extra meat frozen there almost all the time too. Besides, the refrigerator is pretty much always stocked this way, and ready for us to pull out in a heart beat if we decide on the spur of the moment to go somewhere..... works for us!