Good luck in finding a place soon.

As for the other situation, once you have a moving date and have turned in your notice to the landlord could you call the non emergency police number and ask to talk to someone about a possible alteration.
Calmly as possible, practice or write it out before hand do the police will take this situation seriously.
Tell them that you atre moving out on such a date and you are concerned about the possibility of a violent confrontation by a roommate/squatter when you leave. That he has a history of trashing things, owns guns and will be facing homelessness when you move. Ask if there can be an officer there if he will be there the day you plan to leave to ensure your safety? I don't believe you need a restraining order to ask for protection, just the history of police coming to your place and police involment when he has acted up may be enough.