The easy way to the "club":
IXC with 22 eels + port raiding in the Caribbean. Just as Jack Sparrow.
Have done it three times, the result is 350 000 tonnes and 30 ships. There's a lot of tankers, even in neutral harbors! Convoys are also often weakly escorted, even in late war. And, haven't seen a single minefield near the harbors.
Check the place out!
I'm using GWX 1.03.