I always pre-cool in the house refrigerator before loading the RV fridge. But after that I don't worry about putting pulling out a can of soda and replacing it with a warm can.
Do you remember the refrigerator commercial from the 70's where they open the door a a bunch of ping pong balls (representing the cold) fall out? That's kind of the effect you get when you open your RV refrigerator. But unlike a household refrigerator your RV fridge has a slow recovery rate.
What the commercials don't show though is that when you close the door all the items in the refrigerator start releasing ping pong balls back into the compartment. So as long as air can move around the food, the more cold items in the refrigerator the less the opening of the door affects the temperature.