When we moved to this house the only option I had for a pantry was in the garage. I had most of my drygoods in glass jars, but there were a few plastic and/or paper packages as well. I very quickly saw mouse damage/droppings, and once I even saw the mouse. We put a cat flap in the door between the house and garage; for awhile the cats were very interested in that area, though I don't think they caught anything. But in 6 years I have seen no more signs of mice there. I also have put EVERYTHING into glass jars or cookie tins. I know you said that you can't have cats. This comment is just for information, for those who don't think cats will help with a mouse problem. Mine are pretty good mousers, at least a couple of them are, but in an enclosed area I think just having their scent around will keep mice at bay.