Suggestions for improving my watering setup?

Current setup: We have four beautiful hens. We have a small (https://s3.amazonaws.com/images.ecwid.com/images/17432132/1357042818.jpg) metal container right now in our chicken run. It's set up on a small wooden platform that I built, and it sits on top of a water heater that turns on/off via a timer during the cold months (similar to this but different brand/model https://www.picclickimg.com/40EAAOSwewpmTaBO/Chicken-Water-Heater-Heated-Chicken-Waterer.webp). It works, but it's not a great solution.

Problems:

• It is maybe 1.5 years old max, and it already starting to rust along the bottom where they drink from.
• 3 gallons is ok, but we don't have running water out near the chicken run, and so we need to bring this back and forth to the house to fill it up. It's fine in warm months (can fill from the hose), but it sucks in the winter since I need to bring it inside and fill it in the tub in our basement.
• Even 4-5 inches off the ground, they kick a lot of dirt, feathers, and probably chicken shit in here. I spray it out clean with each re-fill.
• The heater barely works to thaw out the bottom so they can drink. It works, but often I find I still need to go out with some warm water to break up the ice a bit.

What I'd like:

• Bigger container
• Doesn't rust
• Rain water collection?

I'm open to any suggestions on products or DIY projects to help improve this for our chickens. Below is a picture of our chicken run so y'all can see what I have to work with.

https://imgur.com/a/D0SmkYn

So, cool chicken-havers of Lemmy... Do you have any suggestions on how I can up my game here? Especially any recommendations on how I can do something to collect rainwater for this. Any guides that may have worked well for you. I'm open to any information.