If you are looking for a more traditional pack, have you looked at Mt Hardware’s BMG -> http://www.mountainhardwear.com/bmg-105-outdry-backpack-OU5956.html . I used one two weeks ago on a 4 day packrafting trip with my two daughters and was pretty happy with the space vs weight. It is waterproof enough I have someone sewing a dry bag top onto the main body right now.
As someone else mentioned, HMG is making a 90l pack, i think it is called the 5400, though it does not appear to be listed on their website. They are for sale in some retail outlets though (Alaska Mountaineering and Hiking carries them for example) so I would give HMG a call and ask if you are interested in them.
I have also used a HMG 4400, and it is a great pack, but not really my “ideal” packrafting pack. From my POV, the perfect packrafting pack would be big enough you can get everything other than the paddles inside it for a 7+ day trip. The HMG is pretty big, but it “grows” upwards and when really stuffed is pretty darn tall, which isn’t ideal from my POV. Possibly the bigger pack would have been a better option for me. The other gripe I have with it is relatively minor – it is a bit of a pain to get water bottles out of the side pockets without taking the pack off. Possibly I just not very flexible.