NO, I wouldn’t try glueing it.
There are various ways to hang a banner, but if you want it done correctly, you must use some form of banner tensioning system and that adds to your customer’s cost. Personally, I would only suggest a tension system if the site was going to be used to continually change the banner/message, or the banner was big enough to warrant one. It really comes down to what your customer is willing to pay for something which is normally looked on as a short-term sign/advert solution.
you could use something like the C-section banner tension system from spirit displays.
To be honest, if the banner is hemmed properly and reinforced with the likes of nylon banner tape, you can fit banners with the likes of tek-screws with their rubber backed washers. however, It really is about your hanging process to make sure the banner isn’t sagging in places like you have said. you can’t just hang it like a sign, you must create a slight taught tension as you proceed.
work left to right along the top but don’t apply all the fixings.
then switch to the bottom with a slight tugging downforce as you fix along the bottom. then down each side.
any areas that are slightly slacker than others can be flattened out by adding fixings in the spaces between your fixings.
if we make a banner this size it normally would have vertical lines of nylon banner strengthening tape down it for the obvious. again, you can run a series of fixings down the strips through the face, as it helps prevent any real wind movement.
banners have a reputation for being destroyed in severe weather and you aren’t going to eliminate that without a tension system of some sort. so its a trade-off, I have fitted countless BIG banners like I have said above, as well as Huge flex-face systems, and also systems like the spirit-flex one. it all comes down to budget. you cannot wave a magic wand for the customer that doesn’t want to pay!