"Q. Can the filter be frozen?
A. While we have no proof that freezing damages the filters we have no proof that it does not. Therefore we must recommend replacing the filter if you suspect it has been frozen."
From article, Roger says when you backflush, the tubes expand a little which helps dislodge any blocked pores.
If the tubes were full of water, froze, and expanded a little it doesn't seem like it would burst the tubes.
Putting filter in your sleeping bag doesn't seem like a very good solution. Hard to reliably keep your filter from every freezing over many trips. Before and after sleeping you'de have to carry it in your pocket?
Too bad there isn't some way to test a filter after it's been frozen a bunch of times.
I am tempted to just shake the filter out really good if it might go below freezing.
Besides, you don't really need to filter the water anyway. This is just a made-up issue so filter manufacturers can sell filters : )