For one weekend, spreading the crack and getting epoxy down in may hold. However, I've had rudders split down the seam on two occasions. Both were Hobie rudders split down the front seam in the area of the lower casting. One was an old-style EPO, and the other was a Hobie 20 rudder. In both cases, I got epoxy inside the split as well as wrap glass around the split (which can be difficult since you may not be able to make the rudder wider). In both cases, the rudder still eventually re-split.

Personally, I would try to get some glass or carbon on the split to help hold it together. There is a lot of load on those rudders. Try to make it stronger than original afterall, the reason it split was because it wasn't built strong enough.

Regarding old epoxy, I've been told that the epoxy/hardener doesn't like to be stored below freezing (32F) because crystalization can occur and thus effect curing. However, if you're epoxy does end up crystalizing, all you need to do is put it in hot water for a while (can't remember if it had to be boiling).

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