I always need at least 5” all the way around for backing/ batting . You need something to fasten to in order to load and quilt. Will your sweet sixteen accommodate a quilt that large? My HQ Avante only has 110” width on my frame. I’ve quilted a couple kings that were 120+” long, I didn’t have a lot of space for quilting design on the bottom border. Seems like you are going to have quite the challenge with this.
I would definitely add some fabric around it to attach to your bars and clamp to