Multiple inexpensive layers?

My friend used this sort of technique on a grand canyon raft trip.
He brought an expensive violin (we enjoyed the acoustics of the walls).

He stored it in the regular hard violin case, then a trash bag with the top tied closed, then rolled it in his sleeping bag for cushioning, then in a dry bag and tied it in the raft.

We flipped once and daily the raft was full of muddy water. The dry bag held out the water just fine and the violin stayed intact.

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Trunk/metal gun cabinet/new garbage can/plywood box/cooler(as mentioned earlier) with dry bag combined with trash bags inside?