I see that putting a fan down near the motor could help but putting a fan on the inside limits the correct storage for many foods, A fridge is not just a cold place to store food, Many foods require being stored at different temperatures which is why the Element in the ARB's does not go to the top of the inner walls because by doing that it creates at leased 4 different temperature zones, Fitting an inner fan creates just one temperature zone so what you end up with is foods that need to be cold end up either too cold or not warn enough and foods that need to be warmish end up too cold. Which in theory means you can only store one type of food, That works ok for a Freezer but not a fridge,
If fitting an internal fan was a good Idea then ARB, Engel, National Luna and Waeco would of done it years ago, The only time fridges are fitted with an internal fan is when one type of produce is needed to be kept at a certain temperature, Or when a domsetic fridge is supplied with a motor/compressor than is not man enough for the job, Having a fan in a domestic fridge again is more of a design flaw and should really be avoided, A fridge should have an internal temp range that varies from zone to zone/area to area by as much as 10*c/18*f and not by 2 or 3 degrees C*/F*.
Because many food types require different storage temperatures does not make it practical for fridges to be fitted with fans because you would need a separate fridge for every type of food that needed to be stored, Which is another good reason why fridges are made the way they are.