I had a pure wooden box on my old cat trailer, and while it began life as sturdy enough for me to stand on, left out to the elements for a season made the top soft, and the whole thing weighted a metric butt-ton. Make sure if you do go wood, you only use it as a light frame that will be covered with glass.
Was it glassed and painted on the outside and, at least, epoxy coated on the inside? You should be able to expect it to last almost as long as the boat if built properly.
How much weight can it handle? Considerably more than the sturdy (as far aluminum boxes go) .090in wall thickness aluminum boxes I built.
