Why should we even want to enclose both ends? After all, we see ready to wear panties with one end left unsewn.
The most important reason is that with one end open, lint and fluff from the washer and dryer can get trapped in the pocket created by the open ended gusset. After all, this is the stuff you have to clean from your dryer - it's not unreasonable to assume that some of it can get trapped in the gusset. Yikes!
The other reason is purely for the pure joy of mastering an advance sewing technique, and when you do, you get that little rush of "YES!" afterward.
Here's my method of sewing a perfect, yet angst-free enclosed gusset! First lay out the pieces of the panty. Have the panty front closest to you with the right sides facing up and the gusset in the centre.
Now flip the gusset upward to the back of the panty with right sides together and pin the curved seam. You will be pinning an inward curve of the panty back to the outward curve of the gusset so it will look like this at the start of the seam...
See where the pin is? That is what I call a "dog ear" and it happens every time two angled seams are pinned or sewn together. The trick is to match the seams at the exact spot where the two fabrics intersect. But...the two fabrics must also intersect at the 1/4" seam line. So it is a definite skill to get it right...but you can do it!
Once the back gusset seam is pinned (no sewing yet!) lay the gusset back down so you can admire your work! And this is only pinned at this stage!
Now flip the front of the panty up to the gusset and pin the seam. On my panty pattern and in my book (Make & Fit Panties), the front gusset seam is a straight line. There is no need to have a curved seam in this area.
Now the real magic happens! Roll up the front of the panty (like a burrito or a jelly roll) so that the pinned seam is visible
Then roll down the back of the panty so the pinned seam is visible. It should look something like this...
Now pin the gusset lining, usually made of cotton jersey) right side down, to the pinned seams, removing each pin and replacing them as you pin the lining to both seams.
OK, now you can go the sewing machine and sew those two seams. You should use a straight stitch 2.5-2.6 mm long and pull the seam slightly as you sew (this is called the "stretch-and-sew method" of sewing stretch fabrics.) Alternately, you can serge the seams with a four thread overlock seam if you have a serger.
So now you may be wondering, what kind of mess you have made. Don't worry! Pull the panty front and back on one side through the gusset to the other side. (it doesn't matter if it is left to right or right to left) Voila! it will look like this from the panty outside...
And like this from the lining side...
So now you know how easy the panty gusset can be! If you are interested in panties or boy shorts - how to draft them from body measurements, fit them, and re-style them into every other style you see in the market, you might consider purchasing my book, Make & Fit Panties