You are going to have to do a lot of cutting on the outside of the trailer, as absorption fridges require outside ventilation. My advice, don't do it.
If you want a fridge, my #1 choice would be to buy a truck style compressor fridge and keep it in your tow vehicle. Alternate is to get portable solar
, and run a portable unit near your trailer when camping (keep it locked). I've been thinking of putting one in my truck bed, and then add a solar panel
to the truck topper. Then I have a fridge with me, whether I am camping or not.
Many compressor fridges are MUCH cheaper than a new 3 way fridge, much more energy efficient too, and they can run colder. They are pretty much better in all aspects.