I picked this Osprey pack up recently in haybale green. It's a 20L size. The fabric has been treated and feels a bit rubberized, so very water resistant; it's slim, interior is easy to see and fits my Rattler perfectly. FYI, the pack doesn't completely open on one side, but I sort of like it that way.
Attachment 83639
All in all, for me, I think its a comfortable, discreet way to transport a Rattler. Bonus, it's on sale for $62.50, which makes it a great value IMHO.
https://www.osprey.com/us/en/product...LDF20_202.html