Thetford fridge shelf

[mr alan]

We have always had the item below loose in our motorhome. I'm sure it's meant to be clipped into something in the fridge but I can't quite work out how or to what, can anyone please advise, it's slightly lipped and has clips on one side only. It's about the same size as the fridge shells but I can't quite work out how it's meant to go, thanks

[nutsytvr]

Cover for the salad (beer) box?