A fire trap CAN'T hit you when you are invisble.
No, there is NO AoE damage, when you are invisble.
Tested yesterday with a botter (a wiz) and i was invisible.
And i informed myself for the pk2 edit to probably get a 'hack' to don't give the others a chance to see me while i am invi. fyi: it's just 1 (ONE!) number you have to change per stealth or invi skill. sick

and no, there is no way to get invi for the pk2 cheaters.
ed: tested while CTF