Joanna Page from “Gavin and Stacey,” and Wynne Evans, opera singer and star of a certain online insurance ad, are in Southwest Wales. Taking turns behind the wheel of a 1984 Mercedes, they sing, laugh and shop their way through the antique emporia, with experts Roo Irvine and Irita Marriott in their wake. They fill the boot of their car with everything from biscuit tins to bowling pins.