I have the Simms waterproof backpack and have been very happy with it. The hip belt isn't as beefy as Patagonia version, but I generally just use the chest strap. With all waterproof backpacks, you need to make sure you pull the zipper verrrrrry tight.
Did a trip into North Belly River last year. Decent lake fishing and fabulous hiking, with many multi day options, including a loop that ends at South end of Waterton Lake with boat ride back to townsite. Highly recommend this area.
Just saw your post. Not sure if it's too late, but I could try to help for a couple of hours Aug 18 or 19. Better option would be to sign up for Simon Gawesworth course the following weekend.