The black foam is the maximum expanding type. You can get it at Home Depot.
While your under there just lounging around :B I suggest you fill any of the exposed crimp connections (clearance lights, etc) with silicone, dielectric grease or something else that makes them water tight. Otherwise the first trip in the rain is going to start corroding these bare connections. Check the behind tail lights if they're exposed. They will be wide open to road spray.
It's reprehensible that NW takes these kind of shortcuts.
