A sealed box using an average of the dimensions you provided, less material (assuming 3/4"), will be around 3.7 cu. ft.. Thats plenty of airspace for most of todays 10" or 12" drivers. A typical 10" only requires 1 cu. ft. or less. With the space available you could build a descent sized vented enclosure.
And it sounds like you have done this before - not many people are aware of the reverse harness idea.
