In the original film just a big strong truck with some chains was enough to rip the shutters off the secured home of the protagonists. And it was rich kids that did it. And the psychos that wanted revenge turned out to be the other rich people in the neighborhood. I think that's accurate because violence usually comes from somebody you know.
This is something that SWAT actually uses in real life when they face security doors that can't be rammed down easily. They can rip the whole side of a building off if they need to.
I don't think most people would want to live in a structure that could hold off a determined attack for a whole day - not to mention it'd probably be against building codes.
Everyone is capable of carrying out such acts, regardless of class. All they need is a chip on their shoulder and an unstable personality.
But, in such a situation, I don't think the rich would go after each other. Yes, it would happen, but it would be for very specific reasons (like sleeping with the guys wife, etc). Even then, people with money usually get even in other ways that don't necessarily involve killing each other. They are more likely to get at someone by hitting them where it hurts. And by that I mean ruining them in business, which equals loss of $$$. A rich psychopath that is hungry for blood will go after anyone, but mainly people that don't benefit him personally (imo). And rich people can benefit other rich people in regards to business connections. Killing each other would be bad business.
Now I agree that most of the violence will come from someone you know. And that would include people that work for the wealthy. My fil was CEO of his company that he sold two yrs back, and he was in charge of hundreds of employees. And everyone one of them had a hatred towards him. They would kiss his ass to his face and talk horribly about him when he wasn't around. You just had to hear the hate in their voices and the look of contempt in their eyes when they would bash him. They would comment on his car, his clothes, his house...everything. One woman even called him the devil. No one is perfect, but he didn't deserve any of that. But they were brought up to have a bias against people with money. Common ones being:
-Money is bad
-Rich people are evil
-Underdogs and the little guys are good, big entities are bad
-You have to sell your soul to get rich
-Money causes good people to go bad
In their minds, (as he was signing their paychecks) he was plotting to ruin them somehow. It was crazy. And I know this because I worked there. These people would say all of this in front of me not knowing that I was dating the boss's son.
My fil didn't have a clue that his employees felt this way. If there was such thing as the purge, he would definitely have been a target. That is why I say the rich should never underestimate a person that resents them just for being wealthy.
And during a purge, the rich people would not stay in their everyday home. They would have a structure built elsewhere for situations like this. People are already building these structures for protection in fear of a doomsday scenario.