Remember you are in Missouri.  That's important because any of us in another state are offering opinions based on our state, not yours.

Regardless of whether he's a PITA the thing is, does he have a valid point? Is residency a requirement not only for your bylaws but per state regulations?  If he's right, he's right

Are you volunteer?  I know in many states that makes a big difference.  We have a new trustee who got to reading Illinois statutes and about had heart failure until I pointed out a sentence near the end that said this section does not apply to volunteer departments.

Is the nearby area in the adjacent state covered by a fire dept?  If so you need to work out a mutual aid agreement so your dept can legally assist them and vice versa.

We have a "watchdog" organization in this area.  It 's actually just a couple guys who only see black and white, no gray.  They don't seem to fear anyone and are more than happy to be a thorn is someone's side.  Your guy may be similar.  The first thing to determine is if he is correct.