Try This Site...
I have a box also and used it originally for a gas tank and other crap. I use it now for spare anchor, dinghy line and disposable propane cylinders and as as a spare seat . I'm guessing, but the width is set across the cockpit benches and the depth is about 16". You can make it as deep as you want. Remember to leave an opening at the botom to allow rain to run down into the cockpit floor scupper. Don
