Dometic fridge problems

The dometic fridge in our new lunar caravan was overwhelmed by the heat last week. Even on the maximum setting it only got down to 15-25 degrees. Surely it should be better than this? What if we wanted to take the caravan abroad? The literature that came with it says it only needs to be on the medium setting when ambient temperatures are in the 15-25 degree range. Temperatures in the caravan last week reached about 32 degrees? Anyone else had these problems? The fridge wasn't overloaded.