As for the wire ties, they work well. One by itself tends to let the edges slip though, so I double over the 'pulled corners' and add another tie just behind the first one. This locks off the corners and keeps the edges taut.
I've used ties on two sub-freezing trips now with no problems at all. If set up properly, the ties (or whipping) don't take any pressure, so there's not much of a durability issue.
As far as getting them good and tight, you can get a wire tie gun ( ~ $10 at Walmart) or do what I do and just use a pair of needlenose pliers. Once you have the tie hand-tight, use the tip of the pliers and twist, which will let you tighten them another 5-6 'clicks'.