Egon and Ray could have built a modified street sweeper for smaller areas of the city where the other Ectos were too big for. Or for undercover, not so inconspicuous work. Plus they finally have a vehicle to clean up excess ectoplasm!
I’ve taken the original 4 page Ghost Sweeper Instructions, scanned them, and made them into 3 PNG files. I’ve also scanned and included the decal sheet.