Some people use storage boxes (of varying sizes – ones with less depth may be better at discouraging cats), but you would need to make an entrance hole in the box and tape the edges so they weren’t rough for the hogs. You could potentially attach the drainage pipe to create a tunnel, although that would be more difficult.
Re. rats, you pretty much can’t stop of them accessing any type of hog feeding box. If you could stop the rats, the hogs wouldn’t be able to get in. But here is a recent series of posts re. rats – you might find something helpful there.