Cut to 5 1/4" long, a 2.5" diameter would tune your box to 34 Hz, and a 2.75" diameter port would tune it to 37 Hz. Parts Express sells 2.5" and 2.75" diameter ports.The minimum length for a 2" diameter flared Precision Port is 5" long due to the length of the flared sections, and that would tune your box to 31 Hz. This would probably be the lowest noise route, but of course it's also the most expensive.
Duke