I recently skinned a new kayak with Dyson's 8 oz polyester, which opens up something awful when you tug on a stitch (or catch it on the corner of your saw horse, or...). I found that it would heat shrink very well however, so I could have sewn it relatively loosely and used an iron to get it tight. Live and learn. One can seal all the stitching holes with sealant, so its not like all is lost. There may be a certain type of seam that is less prone to opening up, but I tried several different stitches and nothing really made any difference.

If you are using nylon, you might not be able to shrink as much, and you run the risk of making the skin loose trying to shrink it, so I'm not sure what else could be done. Sewing the fabric relatively loosely while it is wet might help (so that it will shrink itself when dry) but one runs the risk of it not shrinking enough.

: What is the trick to avoiding all the pulls in loose weaved fabric? Smaller
: stitches? Somethign else?