Hi G, I don’t know the bags you mention but I’ve just got back from an overnighter packing my Watershed UDB. Mentioned it here before somewhere, but now I like it more than ever. It’s a plain 96-litre holdall made from a tough, stiff fabric heat welded and with a drysuit-style zip + basic rucksack straps. You just chuck the raft and other stuff in and zip it up - no need to put drybags within drybags and hope for the best. Should something bite a hole in the packraft you could paddle the UDB ashore. They don’t say how heavy it is, but I’d guess a kilo. Main drawback: $260 - I found mine cheap on ebay.uk.
It’s aimed at sailors, but IMO makes a great packrafting and IK haul sack (ie; open boats). I’ve done a few days packing with a normal rucksack using a giant cheapo roll-top dry bag on the water. It was very comfy on the trail, but the roll-top was splash-proof only; if you flip for long, things will get wet. And in somewhere like Scotland in summer, you might not get a chance to dry out any time soon.