The ballot drop boxes in Washington and Oregon both have fire suppression systems that are designed to activate when the temperature inside reaches a certain point, coating ballots inside with a fire-suppressing powder.
For unknown reasons, the system failed to prevent the destruction of hundreds of ballots in Vancouver, just across the Columbia River from Portland.
Police station would be a terrible choice. People who aren’t able to vote on election day skew poor, black, brown, and/or immigrant - exactly the groups who would be (rightly) afraid of entering a police station.