No matter how you slice it, a refrigerator is going to need to work harder when it is sitting in a hotter environment. The reason for this is the insulation inside is allowing more heat through (as there is more in the air) and thus, the condenser will then need to expend even more energy to keep the interior cold. This concept will apply to your home unit and even one of these car units. Thankfully, though, you can take steps of action in this case. More specifically, a step of action to take. You do not possess the power to control the weather but what you do control is the environment in which you place the fridge. Again, this is where air conditioning will come in handy as you can keep the inside of your vehicle cooler.