I am probaly going against the "norm" here and breaking plenty of rules!
But it has worked for me for 3 years now and plenty of cold beers later!
When I had my trailer tent I simply had a domestic table top 240 volts fridge, which I carried upright in the back of my car.
On arrival at a campsite it was the first thing I pluged into the elec supply. 2-3 hours later it was down to a cool temperature.
I have had a caravan for just over a year now, and I do the same thing, exept I keep the fridge inside the van during transport and then put it in the awning on arrival and plug into my outside elec point.
After 3 years of use it packed up, due to the fact I think, I put it on its side once for a while with out knowing.
I,ve now boughtn another one for just under