Shot this clip to give some tips on how to re set the Contrail taut when it sags.
The first part , pulling the lines in from the outside, is the typical sag you get when the fabric relaxes , that is when it gets cold and or wet.
The second part , pushing the pole up, shows a more extreme sag. That is more than I get from a taut set up in full sun (IE fully shrunk) to a totally wet fabric.
Because I put the Contrail in tension before I go to sleep and at that stage the fabric has cooled down,so somewhat relaxed, that extreme difference has not been my experience except for in my backyard experiments.
If you pull the tent taut 30 minutes to one hour after it starts raining, the sag after that will be minimal and easily fixed by lifting the pole.
Or use bungy (bungee) cords if you prefer.http://www.youtube.com/watch?v=d9VuB5aJ2Rw
BTW, if you do use a fix length pole, lift that and shove your shoe/boot under it.