Writer/Director Ken Wiederhorn was trying to get out of the horror genre at the time Lorimar Productions bought his script. Once the film was released he received nothing but horror-comedy directing opportunities.
The cemetery and storm drain were complete outdoor sets. The mausoleum, hospital, meat packing factory, and interior houses were also purpose-built sets.
When Brenda, Johnny and Ed get out of the car to go into the building in the cemetery, the right front door of the van is open. In the next shot, the door is closed.
(at around 9 mins) When Jesse falls through the coffin in the mausoleum, it is clearly a stunt double. Jesse has blond hair, while the double has dark brown.
The Zombie shot in half had lost his hand in the car window in the previous scene. When he lifts his torso by his hands to attack the gang in the hospital cellar, his hand reappears for one shot. In the commentary, however, the director mentions that this actor was one of several used for multiple scenes. His description suggests that this wasn't supposed to be the same zombie from earlier.