You can park vehicles on top of portals. This will generally make the game crash and also block spawns.
Building a deathtrap around portals is something the community would probably appreciate, illegitimately blocking them with an engine block… probably not.
I don’t know, it seems really dwarven to me. Got a dangerous, lethal portal? Park a truck on it, it’s done!
But yeah, that is kinda too easy. Ultimately, portals should maybe eat the car and get bigger, or just grow around the car, or (my favorite) cut the car apart as it tries to occupy two dimensions at once. Gotta be dangerous, ey?
Last time I checked, portals don’t continuously spawn monsters.