Hi Emmadale
Not sure that a hog would go into a new box, although you might be lucky. But I suspect you might need to be a bit more pro-active. If it isn’t raining (like it is here) and you know roughly what time the hog turns up, you could try sitting quietly near where you feed the hogs. I have done that before just to watch them (put my feet on a footstool) and they didn’t seem to notice I was there. Then you can scoop the hog up and put it in a box (or pet carrier). I would have one ready with either torn up newspaper or a small towel for the hog to burrow under. Newspaper on the bottom as you will need to provide food and water which the hog will inevitably spill. They are excellent at escaping so be aware of that.
I agree, I would get the hog checked out by a hog carer/rehabilitator. You can find the contact details of your nearest one from BHPS 01584 890801. If possible I would contact them before you catch the hog and take their advice about what to do.
You might also like to contact your local Post Office sorthing office and remind them of the dangers of dropping rubber bands. I believe they do encourage their Post-people not to drop them, but a reminder may not go amiss. A photo of the hog might be useful.
Good luck.