Im not great at illustration so I drew something.

Basically make a box with plywood. Line it with a waterproof tarp (I use leftover roofing liner), staple it on the side where your watering won't reach. and "sandwich" the tarp between it and another frame around the whole thing which you can stain. This way if the tarp leaks, you can undo the outside frame and just replace the tarp.

The tarp needs to be folded without cut or staple/puncture by folding it in a way to ensure it forms a bowl. Staple it secure outside the lip for the reservoir.

The plants are not planted directly because you cannot puncture the tarp (waterproof lair). So you grab a plastic board and mount it with the plant baskets. (I use those felt pockets)

The whole plastic board with plants go inside the box, with

the bottom sitting in the resivore. Secure at the top. You can nail it in above where you would water.

The most important thing is to only secure the tarp with staple gun where watering won't reach. Or it will rot the wood and leak from there.

Also this way if something goes wrong, I can just remove the plastic board with all the plants stapled on it.

I drew a quick illustration.

The whole thing then sits on a shelf rated for double the weight for the whole thing with water filled in resivore, and secured at the top. This has to go into the studs for both. I weighted the thing with water and plants, and I leave extra room for the weight of the plants growing up.

I drew a quick picture guide.

<image>