I spent a lot of time looking into this and have spoken to a number of engineers including the Bavaria agents in Hamble, none came up with a simple fix, most wanted to change the unit for a "new up to date one"
When talking to the "Penguin" engineer after I had fixed it he told me he always does that.
First
The heat from the exchanger goes up through holes under the fridge and heats up the bottom of the fridge.
The fan cooling the heatexchanger uses the air that is hot
The heatexchanger gets clogged with fluf
The fix
Cover the holes under the fridge and block off the back.
Clean out the heatexchanger
And the most important, reverse the fan on the heatexchanger so it pulls air off the cabin floor.
I also put another fan in to pull out hot air.
Now runs for 12m and off for up to 55m. remember I am in France and it get hot.
Odysseus