This response came in via email, adding it the list:
What do you use your fridge for?
I am Diabetic. Medication and Ready Use Insulin must be kept below 25 Degrees C in the summer months. (Insulin for use more than a month away must be at 3-4 Degrees C.) I use an Engel Fridge/Freezer which is mounted in the back of a Discovery 4. In addition, it is used to carry food and beverages on trips. Whatever needs to be chilled goes into it. I also use it to transport food etc from the Supermarket to home in hot months like February. The Fridge is dual 12V/240V powered. When it is time to defrost the house Freezers, the Engel is used to store Frozen food for the duration. Ditto in the event of a prolonged power failure.
Where is your fridge?
4WD and House.
What sort of temperature ranges does your fridge typically experience?
The Engel manual, from memory, says that it can handle up to 60 Degrees C when running. Mine is in an enclosed vehicle and could see those sorts of temperatures while parked. On the move the cabin temperature is regulated by the vehicle Air Conditioning.
What do you put in it?
Medication, Food and Drinks. (It is too small to accommodate dead bodies!)
Is your fridge always on, or do you just use it when you need it? When needed. Too much power draw if left on all the time and frequent short city trips undertaken. It is fired up a few hours before going away.
How do you power your fridge?
As mentioned above, it can be powered by 240V mains supply. When in the vehicle, it is powered from 12V Hella Type Power Outlets. (Cigarette Lighter type sockets are prone to overheat when in constant high draw use.) As it may be necessary to leave the fridge running overnight when on trips, the vehicle has been set up with an Auxiliary Deep Cycle Battery and associated Charging System. This preserves the Starting Battery at high charge levels for when needed to get going the next day. Deep Cycle Batteries are designed to be run almost completely flat. Such use destroys Starting Batteries. The Dual Charging System protects the Aux Battery when it gets really low and shuts off the power. It will only connect to the charging system when the vehicle has started and the Starting Battery reaches 75%. After a Day's driving, it should be ready for the next shut down period. The Accessory Power Sockets that are standard in the vehicle shut off a few minutes after the vehicle is stopped. They are no use overnight.
What features are desirable?
Dual 12V/240V power is certainly necessary. For example, the full Fridge could be carried into a Holiday House and plugged in. This avoids having to lug stuff from the car multiple times. Some models also have a third power source - L.P. Gas. I can see this as a boon for people staying off the beaten track for lengthy periods. In my case, I could not justify the extra cost.
Rugged Exterior. My Engel is metal and is quite robust. I can't say the same for the thin paint job. It is too easily scratched. Some cheaper Fridges have plastic casings.
Tie Downs are very necessary. The Engel employs the handles as Tie Down Points. I have installed a Draw System in the 4WD which included Tie Down Rings in the Fridge Slide that forms the top of one of the Draws. Accessory Tie Down straps were purchased to connect the Fridge to the Slide. The Fridge still has a tendency to slide a little from side to side when on the road. It is very important to be able secure what could become a missile inside vehicles. I have also added a Cargo Barrier for safety.
Heating - some Fridges in the market also have a Food Warming capability. Not for me but could be useful for some people.
Lid Opening. The Engel has slide pins on the hinges to enable the lid to be slid to the side. In my case, the lid hinges up and hits the roof when inside the vehicle. I otherwise have to pull the slide out to at he contents.
Plenty of vents. When inside a packed vehicle, care must be taken not to block the cooling vents of the fridge. Having them on several sides helps.
Most Fridges have internal baskets. Internals that can be easily cleaned are important. If not packed well, things can fall over and leak due to vehicle movement. Multiple partitions would be nice to have. A feature that the Engel does not have, but would be handy is a drain plug like some Esky's are fitted with. You mentioned transported of freshly caught fish - I imagine that the inside would get quite messy.