I make weather-stripped plugs for all the drains to the outside. They can be as simple as blocks of wood cut in the shape of the openings, with building felt around the edges as a weather seal. Also, when adding enclosed decks, we put screening between the floor joists and decking. We cover the entire area before we nail or screw the boards in place, creating an invisible critter filter immediately under the deck. The screening will also catch the stuff that finds its way through gaps in the deck boardseverything from earrings to crumbs.You’ll have to vacuum occasionally between the cracks. Think local. How do you find the right storm sashes for your home? National outfits build and sell windows, even some good ones. Small apartment furniture ideas But another option is to deal with sheet metal fabricators locally, or at least regionally. They’ll know about your area’s unique problems and popular building styles. They also will have developed over the years some pretty reliable products. Otherwise, builders would drive them crazy with complaints from homeowners. Take advantage of that experience.