HI bigdog. There are a couple methods you can use. If you want the transom to outlast the Zombie Apocalypse, your best bet is probably to coat it with 2-part epoxy, or to use polyester resin and fiberglass mat to encapsulate the wood. Both work great, but can be a little messy and you generally have to order supplies, but they will last forever (note: you'll want to paint the transom afterwards to prevent UV damage). However, you can get away with using several coats of Spar Urethane, which is readily available at most hardware stores and does not need to be painted, so you can keep the wood grain look, if you want. Regardless of the method you choose, make sure you NEVER use Pressure Treated lumber on a tin boat. Non-PT exterior grade plywood works best. You'll probably have to laminate a couple layers together to get the desired thickness for your transom. Also, make sure you use Stainless Steel hardware throughout, preferably dipped in 3M 5200 marine sealant just prior to installation. That's really all ther is to it. 1.) No PT wood 2.)Epoxy, fglass and/or spar urethane to seal the wood. 3.)Stainless Steel hardware to mount wood to boat.