I have a large Dometic fridge freezer and a wine bottle fridge they were supplied with the wagon I had built last year but I kept an eye on what I was being charged and both models are available for home delivery off the internet.
Get a 3 way one, gas, 240 and 12v from any reputable supplier, either over Internet or caravan sales.
You still need to get it checked once installed, for safety particularly if running off gas as emissions need checking,
Jacksons Camping and leisure have helped me hugely with good products and great advice during my horsebox build...thoroughly recommend them....they also price matched everything I bought from them....