I have the 3M tape and have used it on small things. I think it is a lot of trouble on a long length. For me to use it more I would want a second set of hands. The sail makers use a special "Hot Glue" gun and special glue. One of those would make big things much easier and I would expect a better seam. The special Hot Glue gun is about $1600 and then you have to buy the glue and gun cleaner stuff. To much money for me just doing a few things for myself.
Before I start with a new fabric such as with the Pertex Quantum or when I am sewing two very different types of fabric I play a lot with scrap. I run a lot of different combinations of stitch length and stitch width. I am learning as I go but my seams are looking much better than my first sewed items. For the standard I look at my G6 and the BMW gear I have. I would like to be able to watch the sewing part of who ever makes their gear.
I use Gutermann Thread from Quest Outfitters and good needles. I ended up with a stitch length of 2 and a stitch width of 2 on the Bivy. Sewing machines are different and you need to do some testing to see what you machine setting might need to be.
To Einstein X:
There are several problems with making and selling something like SUL Gear.
1. Getting the really good, light weight fabric for me would be very hard. I was very lucky when I was able to get 10 yards of Pertex Quantum 2 years ago and that may never happen again.
2. Really light stuff isn't very strong and if I was selling anything I would not "warranty" it past your door-step.
3. My sewing skill may not be up to it yet, if ever. Making gear for myself is one thing, making it to sell is a much bigger issue.
3. Time to do it. I am slow and have some other things I want to do before I get much older.
4. Having said all that, things have a habit of changing so you never know.