0.2 Belt and -1knt worth of bulge, also called speedwhoring (as opposed to armorwhoring) is the armor setup you should use on every SN ship as far as I'm aware.
As for getting murdered, well, it's been mentioned that your gunners should have full experts and 100+ vets (overvetting, going over the 100 vet sailor item cap) should make your gunners good enough for GB2 work, you might want to consider trying to roll for more vets if you have excess experts to recoup losses. If you do, make 3 rolls at a time at most and do not let your gunners end up with uneven exp/vets or they will reload their guns at different speeds...
However, the best advice I can give you is that your problem is really your ship and your level, neither of which you can really do alot about. At those lower levels (especially with at-level support and thus low soft defense) you're gonna be easy to sink, what you should improve most is your tactic, hanging back, waiting for bigger ships to become targets before picking your moment to rush, get a shot or 2 in, and move back again. Also, try sticking closer to the middle (I dont mean head right down the centre, just closer than following the line of BBs directly south), its not always so heavily scouted and if you survive to later in the game you might get to move in on enemy ships north or south.
That's just some tips, by no means a definitve guide to GB2s at low level, I recommend you check the old forum data in the tips and tactics section for older BB play guides.
I hope some of this helps.