Sheepskin is the traditional lining for a leather gun case, as the lanolin helped to protect the metal (same reason it was used to line sword scabbards, and the reason some iron swords lasted long enough to be dug up). I would be just as apt to go with a fairly firm foam (say that three times fast
). Any store that caters to campers should have all kinds of closed cell and open cell foam pads, in lots of sizes.
Hard leather cases are often built over a wooden form, and the wood is left in to further reinforce the leather. It won't be a light weight, but I saw a step-by-step description of the process in a book at my local library (Maybe Sid Latham's book,
Leathercraft, but I'm not sure).
I don't like to store firearms inside of cases, socks, scabbards, or anything besides a nice, dry safe. Many kinds of cases can draw moisture, and they'll all retain moisture against a gun that's put away with even a little condensation on it.
Whatever kind of case you decide on, just remember, with Barge contact cement, all things are possible.
Some are just more of a pain in the @$$.
