i have made two smallish backpacks out of some fedex tyvek and tried various tapes since i have no sewing machine [yet -- i'm working on that]. My current version weighs-in at 5oz. [incidently, how do i measure capacity for liters/cu.in.?]
Duct tape: holds well, but heavy.
Low Density Polyethylene Film: holds well and stiffer, but heavy as well.
Tyvek tape: aggressive adhesive, thinner and lighter, more pliable. hard to work with because of strong adhesive. adhesive seems to attract dirt around the edges after use, which is unsightly, but does not affect performance.
I tape both sides of a seam since these were my first projects, but not sure if it is necessary.
I've read that sewing compromises the integrity of the tyvek, so taping the seams helps spread the tension, but have not tried it...yet.
Glue: i've read that others have had good success with 3M super 77, which i have but haven't tried yet.
I've used my bags quite extensively over the past couple months and have been very pleased with their performance in rain, snow and carrying loads up to 20 lbs. The only wear I see is on the straps which have fibers sort of fraying.
for closures, i have been using elastic drawstring up-cycled from an old jacket with it's plastic toggles.
hope this helps you.