Hi Prosecco13
Hogs do sometimes decide to nest in feed boxes. I can see what you were trying to do by hiding the food underneath some straw, but it sounds as if it has just given someone the idea to use it for, at least, sleeping in.
It sounds as if you are quite happy for the box to be used as a nest, but if you ever want one just for a food box, I wouldn’t put any straw, etc. in. They will sometimes spend the day in food boxes anyway, but possibly more likely to if you give them the idea. One hog here made a quite elaborate nest on top of a partially full food bowl once, even though the floor was originally bare (for easy cleaning). I have also on many occasions found a hog asleep in a feed box (when I went to take the bowl out) with no bedding, but those ones have usually moved on in a day or two.
Don’t be tempted to peak into the nest, just in case it’s a female about to give birth. They can desert their babies if disturbed.
Good luck. Hope the hog stays around, but you might need another feeding box!