The housing for the electronics will be an ugly thing. I will go for low cost and the whole thing will be built out of an upside down bucket and a single 45mmx45mm wooden plank that I have lying around. The really ugly sketch below is my first thoughts on the mechanical implementation: There will be the rain water barrel, a garden hose that connects to the ball valve, the solar garden lights fixed to a piece of wood with holes drilled to it and a place to attach the PCB with the electronics. I think the upside-down bucket thing will have the solar lights, the PCB and the ball valve all grouped together somehow.

I have been thinking about if this approach to weather-proofing the electronics is the way to go. I could have purchased or try to make a watertight container or just sticking it into a glob of resin, but in my experience moisture always find its way into everything. I think the solution with the upside-down bucket will cause the electronics to be in very humid conditions from time to time and there will probably even be condensing moisture. However, if I clean off any flux residues, make the board hang vertical so that moisture will drip off and have proper ventilation I might be able to avoid corrosion and misbehavior of the electronics. The circuitry for the ultra-low-power-wake-up will be sensitive to moisture, so maybe that will need extra protection. I am not at all sure it this is the way to go, but I will try it and see what happens. I wonder if morning dew will be a problem inside an upside-down bucket?

Anyway, I went ahead and started building the housing yesterday and it worked out kind of OK. The pink bucket adds a beautiful shine to the whole thing!