My ct kitchen is on the tailgate, too. So easy. My is very basic and consists of the sink, which I have added plumbing to, and a covered shelf underneath, which I have found 3 drawers for. It's so easy to set up and I reckon it would take up far less space in the trailer than a slide out one. If you go back through the ct section, you'll find a similar thread from not long ago and it has some great photos in it too.
Basically, you can have it as simple or complex as you like and can afford.