Water coming in the vent hole:
For something like 40 years now, computer hard drives have addressed the same issue. The drive is in a hermetically sealed can, because even one dust mote or smoke particle entering will cause a
head crash and data loss. But, as the drives spin up from ambient temperature to 5400-7200
rpm they generate heat, the air expands, the hermetically sealed container has to vent and breath--without anything except air passing in.
The vent hole is covered with a sheet of GoreTex material. Air moves through, as it heats, but nothing else does. (Since the
interior is always the "hot" side, moisture doesn't enter)
It would seem fairly simple to "seal" the vent holes in a canister with a more robust version of the same thing, a membrane or membrane plus
passage, that allowed the canister to breath as it heat cycled--but allowed
condensation to move out, and kept water out. If dry packed, or allowed to thermal cycle for a while, there would be no more moisture inside.
And in theory, if the raft is sealed in a mylar bag inside the canister, the condensate is all OUTside of the mylar packed raft, and is just wetting the canister anyway.
Just saying.