Any of the adhesives should work that are comparable to stix-it. Balsa-rite and so on. Some have even used water based polyurethane to stick it down and to fill the weave. I havent so cant comment on how it works, do a search for that. I thin the adhesive with acetone also. Remember that not all acetones are the same. The acetone at Lowes (Crown brand) is too hot and turned my stix-it to cottage cheese. The acetone from Home Depot worked fine for me, not quite as hot. Just paint the adhesive coat on the perimeter where you need to stick it down. I just lay the coverall down and use a small brush to paint acetone on top of the fabric, hold it to the frame for a couple of seconds and it will bond. The acetone reactivates the thinned adhesive. Do that on the whole perimeter. Then I use the iron to slowly shrink it but not too tight, I leave it a little loose. Then paint the perimeter again with the fill coats, only on the perimeter. This will give a good bond. Trim the excess fabric and finish shrinking the interior. Remember, coverall can shrink A LOT. Paint the interior with the fill coat and you're good. If you shrink everything tight before the perimeter is finished, it will loosen up when you paint the fill coat along the perimeter. You cant get a better finish in my opinion. Will never sag unless the internal frame is all crunched up. This is just one way to do it and it goes faster than it sounds here.
Edwin