I have a Camp Trails Moose external frame pack I've had since the mid 80's. Lots on here will probably laugh as it's not an expensive one (about $100 new IIRC), but it's hauled out many moose and caribou over the last 25 or so years. I have some friends of mine that also use the same for sheep,goat,etc. The bag is removable from the frame and made of a nylon type material, but still tough. easy to rinse in a lake,etc The whole pack is very light, not more than a few pounds. I'm not sure if it's still being manufactured.
I've also looked at some new packs lately, but few are external frame and most seem pretty heavy with entirely too many pockets, buckles, zippers and sh!t hanging off them to snag on brush. I was pretty disappointed actually. Maybe someone on here knows of a great lightweight external frame pack that doesn't play to the urban commando or wannabe soldier.