I have put mothballs in a tin cans with plastic lids in antique cars I have had. I cut a small hole in the plastic lid and let the smell out a little at a time. Seems to work but tend to have the lingering mothball smell.
My best solution is to save all my peanut butter jars. Leave the residual peanut butter in the jar. Add lots of mouse poison to the jar. Screw on lid and roll/shake well. The poison sticks to the peanut butter. Remove the lid and the mice devour the poison. I will place 3-4 jars in my large shed at a time. Really eradicates my mouse problems. Also works in the house. Can also just add peanut butter to paper plates and add poison. This works much better than just leaving poison packs out for them.