I was a very young kid when I saw this movie. I was born in 1975 so it had to have been made sometime after that. I can only remember very few random details. I hope I am not mixing memories of more than one movie. Here is what I remember:
1. Setting – warm season, small town or desert-like town.
2. People in a bomb shelter (or storm cellar or basement)
3. Approximately 3-4 men in clown masks with weapons
They’re wearing animal masks, not clown masks, and there’s a part where they’re in a cave and a part where they’re in a dark barn, but not a bomb shelter – but could it be Fortress (1986)? It set in Australia, so the climate/desert like location would be right.
Here’s the full movie: