I've skinned only two kayaks so take what I say with a grain of salt.......I also used Spirit Line's 840 Original nylon.

In both cased I waited to cover until the temperature was about 10 celcius and it was rainy, overcast, humid and damp outside. In these conditions I let the covering drape over the frame for a couple of hours. I then put the covering on and stretched it about 3" for a snug fit on the bow and stern.

I stitched both kayaks up using the Corey Freedman welting cord method. Both turned out excellent.... Corey's method allows for a very good pull in the middle to stretch the fabric tight.

Corey's Youtube video on his covering method....
https://www.youtube.com/watch?v=-bU8Q-TU4Oo