Solar powered poultry tractor

Is anyone a whiz at off-grid solar? I've done some research for a build this winter. I would love for folks to poke holes in my concept. I am still a bit overwhelmed by the options that are out there.

Configurable duck/chicken tractor  

Solar Panel: HQST 100 Watt 12 Volt - Powers water heater (60 watts), predator light (20 watts), electric fence for corn/melons?
Charge controller: 20A 12V/24V
Inverter: HQST 500 Watt
Battery: Expert power 12 Volt 20Ah rechargeable

20Ah is tiny. Do the math on a 60W heater and a couple cloudy cold days and you will see. I use a 115 Ah battery on my trailer with no water heater and no lights (just runs the electronet and the auto door) and if I have a wet rain and lots of ground contact sometimes I need to change batteries (I have a solar charging station that doen not move wit the brds) I have to change it out every three days. I had a 20Ah setup before and the winters were a constant stream of batteries getting manually recharged- on only one net section. Now I use 4-6 100' sections on the big batteries. They charge in 2-3 sunny days with a 100w panel, and with normal weather I only change them every 2 weeks. I expect your water heater would require two full size batteries (drawing 60W 24 hours a day vs 100W production 6 hrs a day?) so would need power management to keep from running all the time. My fence is 1.2 joules and only has a couple milliseconds of charge per second. I would guess my battery rundown with this setup is < 5 Watts. So the water heater >>> than the fence.