> What's about polyester resin?

Hi Ben, I could be totally off, but I'm under the impression that polyester resin,especially bondo like putty, is not at all what you want to seal with.

A very thin epoxy like MAS will actually seal the wood, the turpentine mix is also a decent fragrant traditional sealer. But for minimal maintainance go for epoxy, assuming it won't be exposed to sun.