So Bloodstain Resistant, but with an extra requirement? Don't get me wrong I consider the no armour requirement a good thing - it's far easier to ramp up appearance in FC. I've actually been using Bloodstain Resistant as is in FC since release and had no dramas, so I can't see any mechanical problem with this.
The question is - can you upgrade fittings by themselves? By the book, I'd say yes, but that could lead to some potential balance issues, especially as light fittings are pretty cheap and you could easily stack up a bunch of resistances - the Codpiece of Cold, Fire, Electricity and Divine resistance 4... [pity the man who had to bless it
] It does give me a couple ideas for making a feat chain out of it, but I'll have to check if my idea already exists in the book first.
GURPS has a campaign quality [or their version of it] called Bulletproof Nudity
, which is basically exactly what it says on the tin.