"I have two of your books and I like them very much. My question is about durability. I want to create boxes that are very rugged and durable so they last for at least 108 years. So far, my thinking is that a plywood bottom is not the most rugged bottom for a box with dimensions of 10” x 13” unless you use plywood thicker than 1/8”. Would 1/4” plywood sustain a 250 lb. force from a foot being accidentally placed in the middle? Maybe 3/8” or 1/2” would but then the sides could be compromised by the trench for the plywood. I don’t know. But, I’m thinking that a solid wood panel that covers the entire bottom with an overhang around the edges would be the strongest. What do you think?"Jim, the most fragile parts of a box are the corner joints and the dado cut into the sides to house the top or bottom. Plywood has been around since the Egyptians, but I'll agree that 1/8" is be thinner than what I would use on a 10" x 13" box. 1/4" plywood should offer sufficient strength except in the case of deliberate abuse.
I make my boxes under the assumption that people will offer them reasonable care. Is there a reason you have to suspect that your boxes will no be offered care? There is a balance point. Most of the things you find treasured in museums are not there because they were ruggedly built, but because they were exquisitely crafted, meaningful and beautiful.
My suspicion is that a box showing the maker's interest in skill and beauty will last longer than a box showing the maker's interest in its rugged longevity. We make things to be passed into the hands of others for safe keeping or disdain. There are lots of things that can happen to a box on its way to 108 years. Like the landfill?