As a plein air painter and woodworker, I've been building and enjoying my own pochade boxes for years, while always thinking about how to make them.
From my experience, I've designed a line of pochade boxes that incorporate all the features that I've always wanted.
I'm happy to make these paintboxes by hand, following a business model that lets me interact with my customers personally and be responsible for the last details of construction and design.
The drawback of course is that at times demand exceeds supply, and I get backordered. My lead times typically run from two to six weeks. Just drop an email my way and I'll let you know what the wait time is at the moment.