British tank stowage item identification

[Jakko Westerbeke]

That is proving difficult to find a picture of, because the combination "victory" and "kit" results in a ton of hits for model kits of HMS Victory while adding "sleeping bag" produces all kinds of modern ones

But I think a sleeping bag is unlikely. Somebody on Missing-Lynx suggested a British officer’s sleeping bag, and I don’t think it’s that because the shapes don’t match. Plus, it seems an odd place to stow a sleeping bag, right where it will catch as much dust as it possibly can.