Sorry. I was too with my last comment.
Appreciate the reply, Jeff, but I've gone with Dave's design and Jim's suggestion of plywood panels. Parts are already rough cut.
The purpose of a dock box is to store boating and fishing supplies/tools you're not going to need while at sea, but want handy when cleaning, doing maintenance, etc. at the dock. When I say "at the dock", I'm talking a slip in a marina. It helps get clutter and weight off the boat. To modify an old military expression: Ounces make pounds, pounds burn fuel.