"I've always dusted the seams I've sealed with a bit of climbers chalk."
Excellent. I'm not a climber but a friend left his climbing bag at my house recently. I zipped it open and presto! climbing chalk right on the top. I dusted the seams, so we'll see how that goes.
"Given the lack of stretch of cuben, have you noticed any difficulty maintaining a taught fly?"
There's not much you can do about the taut-ness of the fly one it's built. If you nail the shape during construction, then it'll be perfectly taut every time in the field. If the fly comes out a bit saggy in areas, then no amount of additional tensioning is going to significantly improve that. If it was really saggy, you could probably cut and overlap the material to remove some sag. Essentially, cuben requires more attention to detail during construction than nylon, but it also rewards you with an excellent fitting product if you get it right. Once built, it is what it is. For my fly, most of it fits excellent. The only area that is a bit loose is the left side of each vestibule. You can sorta see this in the picture below. Thankfully cuben is not a noisy material (unlike spinnaker), so it doesn't really matter if this flutters in the breeze a little.
"Any thoughts about replacing the floor of your tent with cuben as well? I have been searching to see if anyone has done this and whether they have durability concerns and difficulty bonding/sewing netting to the cuben."
I've been mulling this over. My inner tent (21oz) weighs more than everything else combined (fly, poles, stakes, tent sack). If I had the skills, I would love to remake the entire inner tent in solid (0.45oz?) cuben, and then I could actually sell the original tent since I have Fibraplex poles too. The problem is that sewing is a weak skill for me, and the original inner would be pretty darn hard to replicate with it's circular door zips and countless clips to attach it to the poles etc. That has me thinking about just replacing the floor.
If I did replace the floor, I would leave an inch or so perimeter of the original floor still attached to the netting walls so I've got something stronger than netting to attach the cuben to and so I wouldn't need to resew the zippers. FWIW, Zpacks has made some Hexamids with cuben floors sewn to the netting but I haven't seen the details of the construction.
If I do it, my basic approach would be:
1) Acquire 3 yards of 1.5oz (not 0.74oz) cuben from Zpacks ($87).
2) Turn material into a basic rectangular tub shape by folding it at the corners and sewing (or bonding or both). Seam seal if necessary.
3) Reinforce corners and then add stake out points with grommets for the poles to attach to.
3) Probably unnecessary, but I would fold the top edge down with a 3/4" overlap and then bond this to double the thickness where it's going to be sewed to the rest of the inner.
4) Cut original floor off of the tent, leaving a 3/4" or so perimeter to sew the cuben to.
5) Sew new floor in place with a few rows of stitching by sewing the double thick 1.5oz cuben to the remaining nylon perimeter of original floor. The would be extremely strong and in no risk of tearing out or even enlarging the holes.
You could do the same thing with lighter cuben, but 0.74oz cuben uses mylar membranes that are only half as thick, so I'd have some worries about abrasion leading to the cuben delaminating. If you always use a groundsheet, you could likely do this. I don't use a groundsheet.
One of the things holding me back is that I don't know how much my current floor weighs. All the REI website says is that it's 'coated ripstop nylon. I used their Live help and the rep told me that it is 30 denier nylon. That seems a bit light to me (I would have guessed 50-70D), but if it's true then the floor likely isn't much heavier than 1.5oz/yd now. What is 30D PU coated ripstop nylon? 2oz/yd? 30D silnylon is only ~1.5oz/yd. If they're right and it weighs 1.5-2oz/yd then I'm not really save much weight. However if they're wrong then I could potentially save 6oz if it's 3oz/yd 70d nylon.
My tent floor is approx. 84" x 50" plus a 4" bathtub equals 5336 square inches or 4.1 square yards.
Regarding the actual performance of 1.5oz cuben as a floor, I like that it would be entirely waterproof and that it's no more slippery than my current floor. Slippery-ness really annoys me with silnylon. My only concern would be the abrasion resistance of the bottom mylar layer. I think it would prove to perform adequately well in this area, but we won't know for sure until more people are using it. One could always keep the original floor on hand to sew back on, should the cuben prove unsatisfactory.
