If you want an animated texture, then use a static mesh instead of a blocking volume.
You can scale them be as big as you want them to be, I don’t understand.
And maybe use the Opacity pin in the material to make it “fade in” when you get close to it (based on the world position of the camera), so it won’t feel like you’re in a confined space all the time, only when you approach it. That being said, there are other, more organic methods, of keeping your player interested in exploring inside the map instead of outside it. Block them with a mountain, with parked vehicles, with fallen trees, burning fire, cliffs, roads that were caved in, ravines, a body of water, pieces of a building that fell down, fences from a nearby park, anything would be better than breaking the illusion that you’re in a video game with running into an invisible wall that has a scrolling texture on it. Come on. You should take a look at how similar games in the same genre deal with keeping the player engaged and prevent him from running off the map.