"What did you build that out of to make it weather resistant?"

I used some scrap lumber I had around and covered it with some of that wavy (corrugated?) plastic greenhouse panel stuff. BTW, when did plywood get so doggone expensive? It is not completely sealed since it needs to vented due to the gas fumes, but I figure that as long as I keep the rain from falling directly on the (plastic) gas cans, then that's probably good enough. It also keeps the dogs out...