Grant Erwin writes:

The answer is to fabricate one, which I can certainly do. I'm
wondering if other guys have "been there done that" and can give me any
pointers.

I've bookmarked this for a while:

http://www.plansandprojects.com/portable.htm

The problem with this type of thing is that any error in design or
execution is a potential disaster, assuming you use it at the capacities
you're describing.

The problem is one of engineering, so I would be leery of any design that
wasn't "engineered" in the strictest sense of carefully calculated and
tested, not just guessed at or overbuilt.