We've built a few different styles now. Our newest versions made of local Douglas fir. We get the wood from a local mill rough cut into 2x4s. Then we use a shaper to make cup and round-over edges on each of the staves. The bases, also doug fir, are cut to a double tongue and groove, fitted together then cut round. We use a similar v cut like the cruz on a traditional barrel for the joint between the staves and base. The hoops are made from 1/2" soft rolled steel rod rolled in a conduit roller and threaded at both ends. The whole thing is assembled squeezed and filled for swelling. Pic is of a couple unassembled vats. As a disclaimer, i need to note that we do use hardware to afix crossmembers on the bottom, but we use stainless and does not ever come into contact with liquid.