I won't go into the details*, but I've decided to go back to a "sawhorse" configuration for the legs. It's cheaper, very strong, and easy to build.
We're all too close to the process to have an opinion now. What do you think of the aesthetics?
Top, old sawhorse supports; middle, concept for detachable legs; and bottom, for new sawhorse supports. Do you strongly favor the look of the middle design over the bottom one?
After all this I suspect most people won't much care! Thanks for your help.
*If you're interested; our calcs for static loads on the box with the a few people leaning on it top 700 pounds. There can be tremendous side loads on the legs . This requires some very substantial attachment points on the box bottom, increasing weight and cost; in the end the horse configuration, while not as clean-looking as single legs, probably cannot be beat for weight, strength, and cost optimization