12. Seal Cracks and Use Weatherproofing
One of the side effects of cutting out any section of a shipping container is that it leaves large cracks that need to be sealed. You can accomplish this with caulk, spray foam and backer rods. Alternatively, a welder can bring the side gaps together with beams.
After the cracks are sealed, you will want to put steel wool in place to prevent mice from entering your home. Next, you can use sheathing for weatherproofing. And, of course, you will want to ensure that everything is attached together with the appropriate deck screws and bolts.