My 2001 Bigfoot has I think a Dometic fridge and my first couple of short weekend camping trips usually resulted in sort of cold fridge that left me frustrated. I even took the unit in to be serviced but other than just a good cleaning, the shop said it worked fine. What I realized is that I had a tendency to heat soak the fridge when stocking it up on Friday afternoon. The combination of having the door open to load it and the amount of food that all needed to be chilled back down was too much for it to overcome, especially if I only turned it on a few hours before.
Here is my current strategy... My truck and camper stay at an indoor storage facility. I'll have them pull it out on Wednesday or Thursday (at the latest) and I'll go over and turn on the fridge. I keep several cans of Pepsi in the fridge and this is a key part of the strategy... These fridges work by radiation. That's why they have no fans inside, just the metal fins. The Pepsi cans act as another source to radiate (when they are cold of course). Leave the fridge on for 24 hours to 48 hours and the fridge will be nice and cold along with the Pepsi. Now, when you go to load it up on Thursday, your going to have that door open and a bunch of sort of cold food from the grocery store. The cans of Pepsi help to act as a "reservoir" of cold that once the fridge is stocked, can help to cool the rest of the fridge back down. Now, the Pepsi is just one strategy and I'm sure if I looked at the math, probably just helps a little but then, being able to grab a cold soda after hitting the grocery store to stock up for a weekend is worth it...
That being said, the next step in my strategy is to fill one of the lower food bins in the fridge with a small bag of ice (remove the ice from the bag). If you really want to help things out, get a small 5v USB fan and place it on top of the ice with the fan blowing over it. This will help to get the fridge cold in a few hours and help to keep it cold when stocking it up. Just be certain to empty the bin before it turns into water (usually lasts a weekend).
Lastly, it's well worth it to get a remote temperature gauge to keep an eye on things if you suspect you are having trouble. I have a simple oven thermometer in my fridge that stays there because it's simple and idiot proof but if I'm suspecting trouble, I'll throw my remote thermometer in the fridge so that I can check the temps without having to open the door. Opening that door every 30 minutes even just a hair to check the temp will compound your cooling troubles.
