Anthony,
If you are able, try mounting the system in your shed, if that is going to be its permanent spot. Mine is mounted in a 12x24 storage building about 50 yards from my house. It has electricity. I am using an Apple Express as the wireless connection to my WiFi, and have not had any problems with this setup. As for temps, it reached 111° in the shed last summer. I have a fan on a timer to cool the Express. The max temp I saw on the CPU was 52°C. The thermal tolerance on the parts is 70°C, I believe.
On the ground, I pounded a 6 ft. rod into the ground next to the shed, drilled a hole just large enough to get a piece of 12 gauge wire through to the rod. Once I was satisfied with the connection, I sealed the hole with caulk. To connect the ground wire to the controller, I got a short piece (like 6") of 18 or 20 gauge wire for that and connected it to the 12 gauge using a wire nut. My signals went from looking like yours nearly to what you see on mine now. Check the signals at sferic.us, through the forum. I need to buy a decent power supply for the system, but finding one that will take the heat and not cost a fortune is a trick, so the iPhone power supply has stayed.
John