Diagram of the block at the cranse iron, thanks to Rod of BCC
Iduna
A rolling hitch or one of its derivations seems to work fine for a lot of people. I use a simple 2:1 slipper tautline hitch (with the bitter end tucked through the bight)0, and it has never slipped. I usually use 1/2" nylon, but as per your question of storm conditions, would probably use a long length of 5/8" for its strength due to loss in knots and contact points. The hit should hold though.
~Aaron