If you've got an outdoor plein air easel, putting your supplies somewhere is an issue. Other than setting your boxes on the ground or on a flimsy support, consider these easel butler arms as an alternative that may work for your setup.
Home-made watercolor pochade box. I'd made a similar box for oil, and thought it would be fun to make a few small changes to hold a 9x12 watercolor block. It is made from two unfinished 9x12 wood frames, which hinge together. Position is held via a pair of adjustable friction hinges. The box is shown atop my tripod from Guerrilla Painter.
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