Try some hose clamps. Bout 3 down the barrel should do it.
I wish I had a camera with me 4 years ago at an auction I went to. The ad said barrels, locks, handmade guns etc... The handmade gun was built around/onto a rough cut piece of high grade pine, roughly the size of a 2X4, the butt plate was not filed, just held on with flat head wood screws. Same for the trigger guard and lock. The barrel was, in fact, held on with hose clamps.