Add a power source to a fridge van

The Build
1

So basically I have a fridge van. But I want to add the feature of adding a power source. So this will allow me to plug the van in when the engine is turned off to keep the food in the van cold. I’m wondering is this a possible job? And how to do it

2

Extension cord from the fridge to the plug?

3

But it doesn’t have the feature to plug it in. So what do i do?

4

I think we need a better explanation of what you have.