Are you saying there's only 30mm between the chainstays?
Otherwise I'd guess that 42mm fenders are the widest that will fit between the chainstays/caliper brakes.
32mm tires may be as wide as you can go aswell.
Be sure to try the tires, fenders and brakes together before committing if possible.
SKS Bluemels come in Silver 42, 45 and 53mm.
I'm basing this on similar frames I've owned, but not identical to yours