yes i know this is probably on this forum somewheres...but i didn't find it myself...so can someone please tell me if i may use barrel behind the door as a chain to immortal of thunders effect?

No need to search the forums, since it only requires to be searched in Immortal's or Barrel's official rulings:

[Re: Barrel Behind the Door] "Barrel Behind the Door" can only be activated against DAMAGE. It cannot be activated against costs like "Imperial Order" or "Wall of Revealing Light". It cannot be activated against effects that cause you to lose Life Points like "The Immortal of Thunder". It cannot be activated against effects that switch damage, like another "Barrel Behind the Door", because they do not inflict damage, they simply transfer it.

alright then:)............................