Scott, Go thinner if you can. The gasket will compress with use and can vary your z. so go as thin as you can and still make a seal. I am using 1/16th inch that comes by the foot in 12 inches wide. It seals just fine with a joined piece of wood. The only issue I've had has been that some woods will lose vacuum right through the wood. If this happens I use clear packing tape on the bottom of the piece. Seems crazy, but it does work. Wouldn't trust it to any heavy cuts though.
David