I made this box with the plans from http://www.pochadeboxpaintings.com. I changed up a few things like making the box smaller and adding the wet panel carrier to the top. The little piece to adjust the panel carrier to accommodate smaller panels is just an extra piece I had left over from cutting the sides. It's fit in there with friction but if I need to, I can stuff paper in the side to keep it in place. If I were to make the box again though,I would change two things.
One is to use a thinner piece to support the T-nut and mounting the nut from the inside. That way, when the box is screwed to the tripod, the bottom will fit flush and the pressure will keep it more stable. I had an accident where the nut came off the box since the friction isn't enough to make the nut stay put on the box.
The other thing is to make the spacing between the inside part of the lid and the space where the first panel will fit in thicker. Right now, with the clips in place, I can only use the furthest notches to hold panels since the clips take up a lot of space inside.
Images below and a test run!