FWIW, it’s been a long time since I tried, but I never had much luck (mis)appropriating non-gun designs for use in carrying rifles. Tried various sports bags, duffle bags, tool bags… I always came back to wanting a bag that looked like it wasn’t a gun bag but performed like a gun bag inside. Among the issues I recall were a lack of toe-down straps in the bags in ci junction with strap-attachment systems that weren’t designed to carry the weight distribution of a rifle, and then of course most of them requiring the rifle to be broken down, which is generally non-optimal to me, but then also lacks dividers. Yes, I’m sure I could spend a bunch of time fiddle-farting around to press a $100+ well-made duffle into service to do all of that, or I can just buy the right tool for the job.
Of course, I’m also not trying to sneak around with a rifle. I just prefer it not be totally obvious that it’s a rifle going in and out of hotels or (at the time) in front of the neighbors in a zero-lot-line neighborhood. Although, in that circumstance, it was pretty amusing to have a nosy neighbor walk over and say “whatcha got in the bag” and me reply with “machine gun and 500 rounds of ammo”.