You have done quite a service in bringing this to our attention, as a heads up to other folks working with Cuben. Much more informative than the pic that Ryan posted a couple times. Hope you will take Roger's and others' similar advice.
Taping is fine, but in a lot of tests I've found that it has very little peel strength, and may not relieve stresses on the stitching created by the conditions you describe. Cubic Technologies uses a proprietary heat-based process to get the PET, or Mylar, to adhere well. Tape is a poor substitute.
So I've concluded that I will not put Cuben into a sewn seam without folding over the edge going into the seam into a hem, inserting a strip of sub 1 oz PU treated Dupont 6.6 nylon, like Porcher Skytex 27, and bonding the sandwiched hem with Hysol 2-part urethane low viscosity adhesive. This is not a a totally peel strength bond, but is the best adhesive I've found for this after testing a couple dozen of them, and appreciate the help of Lawson and others in posting about the Hysol.
I imagine clamping will be necessary also, making the process daunting enough that I've decided for now at least to use the silnylon Thru-Hiker sells for the next MYOG shelter. It will add almost 4 ounces over Cuben to the shelter, have some sag as the temp drops, and I don't like TH's color options (I went for a Coyote brown canopy for stealth, and a orangy "sun" yellow floor for not losing stuff), but tests by a number of contributors to this forum showed it to be far superior in water resistance, and I've found that its sag factor is much reduced also, to about the same extent as some of the softer paraglider fabrics I've tested that are treated to reduce sag but are less water resistant. The Dupont 6.6 nylon is also very strong for its weight. So I think the almost 4 extra ounces for the "Shield" silnylon is worth every gram. Who knows, maybe I'll get to love a brown tent. Silnylon is thin enough that plenty of light will come through, and the orangy yellow floor will brighten things up.