Added 11 minutes later
enchanted armor won't let it buff,
alternatively, to make it vulnerable, you need:
1) 4 immunities to elements
2) immunity to mind control
3) 2 immunities to berserk/subjugation from Sandro's cloak (only confusion and fear will work under the cloak)
4) immunity to weakness, slow, and blindness
5) 75 armor
With this, it will be vulnerable to some damage, but the original doesn't have immunity to 4-5th level spells, so 75 is even excessive, as is fire immunity, because both the original and your version suffer from fire shield (and should).