Code:
 on !*:join:#:{
  .hinc -m Watch $+(Nick.,0)
  .hadd -m Watch $hget(Watch,0) $nick
  part $chan
}
on *:start:{
  .hmake Watch 10
}
on *:connect:{
  .timer 0 300 watch
}
alias watch {
  var %a = 1
  while %a <= $hget(Watch,0) {
    .enable #watch
    .whois $hget(Watch,%a)
    inc %a
  }
}
#watch off
raw 301:*: halt 
raw 311:*: halt 
raw 313:*: halt 
raw 312:*: halt 
raw 330:*: halt 
raw 319:*: { 
  if !$istok($3-,<channel>,32) {
    .join <channel>
  }
  halt 
} 
raw 318:*: .disable #watch | haltdef 
#watch end


You'll have to replace <channel> with the actual name of the channel you want to monitor