TaM
Sorry I missed your comment but I see that Mary was onto it.
Yes, strangely enough my lawn can produce more condensation than most camp sites, hence it is a good humidity test.
It also happens that every so often we get some very good hard and wind blown rains, so that is good practice too.

Mary's (Oregon mouse) advice is spot on as usual.
The trick in counteracting sagging is to tighten the tent when fully relaxed. So you set it up taut, than if it gets cold or start to rain it will relax.
After a while there is no more to give , IE the silnylon is fully stretched. This is when if you put it in tension again it will stand up perfectly taut all night.
I have installed shock cords in the Contrail but I can get a tauter shelter with just the standard tie-outs pulled in correctly.
BTW, when you read someone saying that they had to re-tension their shelter several times, what they are really saying is that they are not doing it correctly...
(same as in :I had to do my shoe laces up several times....)

Claus
Freestanding...
I should have mentioned that, since I do have that pole.
My point is that as it is it takes less stakes than most "freestandding" tents anyway.
There is one brand that advertise their shelters as "freestanding" and that is true for what Americans call "tent" (we call that a bug net) but once you put the fly on it takes 11-13 stakes to make it work.
Franco