The backyard solar shower was well over ten years old. It had served us well but it was starting to fail. Two pieces of plywood were actually not plywood but OSB or chip board. This wood which supported the glass "green house" case around the water heater had begun to sag substantially. Grape vines also had grown over the plumbing. Earlier, in cleaning up the grape vines, I accidentally yanked on them too hard, not realizing that they were wrapped about the plumbing. I broke the CPVC plastic pipes. Crap! There was no fixing this without completely rebuilding everything.
Below are some "before and after" shots of the hot water heater. I made some performance upgrades to the new system. This time I stacked the old RV hot water heater tank on 2x4s a little higher. This lifts the tank where it will be marginally warmer. Also I glued foil-backed styrofoam to the back wall. The foil should reflect light/heat back better on the tank than before when it was simply white plywood. The insulation will--of course--insulate. I also stuffed some of this insulation under the tank.
The replacement sheet glass on the top is larger now. This, I hope will provide a drip edge, shedding water away from the plywood to help preserve the green house case a little longer. We'll see.
The heater's biggest weakness remains that the tank is simply too small. There's plenty of opportunity for a larger tank to heat up. The small tank just runs out of water after one person's long shower. I searched around Craigslist for a dead small (but larger than currently in use) hot water heater that I could use but, with summer here, I lost patience. I wanted my outdoor shower to come home to when I got off work after an uphill bike ride. I now have a shower back to plunge into for sauna sessions.
One additional observation: Silicone caulk is amazing stuff. (Maybe so much so it's a little frightening.) The sheet glass that I glued/caulked together 10 years ago is still holding up fine. In fact, as you can tell from the photos, I didn't take the glass enclosure apart really. I only removed the top piece. The silicone was so resilient that this proved to be a real challenge and I ended up cracking this sheet of glass and had to replace it. Otherwise I simply cleaned up the three glass side walls and reused them as is. Maybe I'll insulate the pipes coming out of the tank too?