Thank you for your inquiry about the super annoying brown marmorated stink bugs (abbreviated BMSB, the scientific name Halyomorpha halys) which hang out in and on selected structures during fall. You can minimize their numbers but, unfortunately, you won’t be able to eradicate them. No one can.
They are staying in the wall void where it’s protected and relatively warm. On warm days, they go outdoors to bask in the sun. When cold weather sets in, they may migrate indoors.
Effective “fight-back” strategies against those spending the winter at your place include sealing/caulking all possible cracks and crevices indoors where they are entering. (Wait until July to caulk and seal cracks on the exterior.) Vacuum any that get indoors, or flick into soapy water. If they’re particularly numerous, use a wet-dry shop vac.
You can trap any that come indoors with an easy-to-rig device. Add about an inch of water to a large rectangular foil roasting pan, plus a drop or two of liquid dish-washing soap. Set in a dark room at night, with a desk lamp shining onto the water. (Use a regular bulb, not an LED light.) Empty the trap in the morning, then repeat as needed. See “The Perfect Stink Bug Trap Is All-Natural” (http://wvtf.org/post/perfect-stink-bug-trap-all-natural).
Fortunately, BMSB don’t feed or breed during the winter, nor will they damage people, pets, or structures. Then, too, it’s worth knowing that insecticides, including bug bombs, won’t help.