Some years ago, when I used a Gregory internal frame pack (which is a nice piece of kit), I did not like the performance when loaded with more than 20 kg.
Too much pressure in the middle of the back. And: I like the backpack to be
waterproof. Traditionally you take a second lightweight waterproof bag inside
of your backpack and use it as top-loader. But I don't like that:complicated and heavy.
So I started to look for waterproof expedition-backpacks and found nothing good.
I always used an ALICE pack for short trips and decided to go for a big external
frame pack. Since then I use a Haglöfs Alaska frame, I removed the sack and
combined the frame with a 100 l waterproof Cordura bag.
For me this is the perfect combination. I think I will never carry anything else than
external frames any more: the advantage of using it as a Kraxe for wood (or game if you want) is impressive, my back loves it , it is simple and very durable.
The waterproof bag is a great plus too. It is not heavier, although it is made of
heavy Cordura, because I spare many small waterproof bags and bottles.
And it's my conclusion from experience with vermin and Monsoon. (How about
jumping into a river with this kind of backpack? Of course it swims, but the real
plus: you don't have to remove it, works like a flotation vest)
I even tried to get a Norrona frame, but the company salesman-idiot told me, they
don't sell the frame only. Anyone an idea where to get it?