How about a boat like CLC's Chesapeake 16 or 16LT? Fly fishing seems to call for a boat with a little initial stability and 5-day trips call for a bit of storage volume. On the other hand, your weight doesn't dictate a very large boat. I think the Chesapeake would be right at home in the wind and waves you describe. And it probably is fast enough for the times you want to cover some miles.

The challenge might be to build it to the weight you are looking for.I suspect you might be able to bring the weight under 40 pounds by watching the fillet thickness and end pour size, and maybe going to a 3mm deck. You might also consider going to a lighter (4 oz.) fiberglass sheathing and maybe not sheathing the entire hull. (Perhaps just up to the waterline.)