Good call. Cardboard boxes make great hides - cheap to throw away when they get dirty and easy to replace. You usually don't need to clean or sterilise them. The only problem would be if they'd been in contact with cleaning products or other household chemicals - in which case, just use a different box.
With Corns, the more hides they have, the happier they are. They don't care whether you've spent £5 on it, or caught it for free before it reached the recycling! Toilet roll and kitchen roll tubes also seem very popular.