I wouldn't go overboard with the strething routine. I have seen lines where the core stretches but the floating sleave eventually retracts to 'normal' and the line becomes curly. I have left my lines on the reel at the cottage over winter and they are fine in the spring when I return and the weather is WARM. I would just put the line in some warm water and then lay out or put over a couple of doorknobs in loose loops.
As far as cleaning, I suggest some warm water, soap, and a soft sponge. The sponge should pick off some dirt but not srape off the finish. I guess in the worst case you have a sink-tip line and have learned a lesson to clean after every trip. Cheers.