UH, Your string stretching is not really a problem hunting in the rain. Keeping a good coat of wax on the string is a good idea at all times for proper maintenance. Just be sure to dry and inspect all your gear well if you have gotten it wet before putting it away.

A larger consideration hunting in the rain would be losing the bloodtrail, making it harder if not impossible to recover the game. The largest factor to not hunt in heavy moisture.

Aim Hard!