Something

on *:JOIN:#:{ 
  if (%voice == enabled) {
    mode $chan +v nick
  }
}
on *:text:!av on:#:{
  if ($nick isop $chan) || ($nick ishop $chan) {
    set %voice enabled
    msg $chan Auto Voice has been turned on for $chan
  }
}
on *:text:!av off:#:{
  if ($nick isop $chan) || ($nick ishop $chan) {
    unset %voice
    msg $chan Auto Voice for $chan has been turned off.
  }
}