We have tried several and they just don't seem to be standing up to the vibrations here. I wondered if there is a better option. Currently we have one made by Thomas EMS.
Those Engle fridge/freezer combos are extremely rugged. They were commonplace in every expedition vehicle I've ever seen. However, to keep your Ativan and sux cold, probably a little bit overkill. The service I worked for, before SCEMS, just used a small El cheapo cooler/fridge from JC Whitney. About 100 bucks. When they would stop working, they would just toss it and buy a new one. We had a small box for the RSI drugs and benzo's that lived in it.
We have Norcold fridges in our ambulances, I think they're designed for boats. Ostensibly they are for the RSI pack and racemic epi, but they are also great for storing ice cream found in hospital EMS rooms. They fit perfectly in the pass through that no one uses anyway.
We use Engel 15 digital display coolers that will regulate the temperatures on its own based on the temp of the truck during the different seasons. It does need to be plugged in though. We store our chilled NS for therapeutic hypothermia and it lives in the pass through