As said above you need a fixture with a 1/4-20 thread on the boxes bottom. The fixture needs to be flush with the boxes bottom so you need to drill a hole in the box when attaching… say the Judson device. This fixture will allow the tripod to screw onto the box…. but.
Then you need some sort of tripod quick release-lever gadget to make that handy to do. These are sold at camera shops if your tripod did not come with one.
I’d also mention when locating the fixture, put it at the point of ballance when the box is open and a panel and the boxes contents are fitted to it. This will be further towards the back then at first you’d think. That will help keep the box level in use. Enjoy!
-Dave

you can buy a 1/4×20 threaded socket piece at most hardware stores and figure out your easiest way to attach it.

An alternative to drilling a hole in the box is to mount a threaded insert into a piece of wood, then epoxy that piece of wood to the bottom of the box.
This is how I usually mount a homemade tripod mount to a homemade pochade box.

Ace hardware has two styles of The nuts. One has little tabes made to be forced into the wood so they don’t move. The other has a larger flange with holes and gets screwed to what ever ya want. That would require drilling holes in your box or attaching something on the bottom.

Donald

I made a tripod plate out of a piece of hardwood flooring sample from Home Debpot ( Free or 25 cents depending on your home depot) and a 75 cent 1/4 – 20 threaded T-Nut. Remember that the T-Nut has to be installed so that the plate side is on the opposite side of where the threaded tripod attachment enters. I also bought the Guerrilla painter version, but ended up not using it as my home made one looked and fit better. I used permanent glue and small screws from the opposite side. It will never come loose without breaking the board on the bottom of the pochade box.

Ace hardware has two styles of The nuts. One has little tabes made to be forced into the wood so they don’t move. The other has a larger flange with holes and gets screwed to what ever ya want. That would require drilling holes in your box or attaching something on the bottom.

Donald

Yes, those are the two standard hardware T-nuts available everywhere.

Whatever you do to attach it to the bottom of your box, you have to make sure that the bottom of the box is stiff/sturdy enough to handle the load and lateral forces.

I made one out of a tabletop box whose bottom of plywood needed reinforcement across the whole width in order to withstand the forces. On the other hand with a lighter kit that I made out of a cigar box, all I needed was another piece of wood about 2″ square. The difference was the size and weight of what sits on top of the tripod. The larger in any dimension the box and/or the heavier the load, the more you need to ensure reinforcing the bottom with your T-nut centered on the load NOT the exact center of the box necessarily.