I found this website today for the H2orse Animal Watering System.
My first thought when seeing this waterer is that it may be the perfect solution to both hauling water from home, and watering back at the trailer when finished riding for when we haul out for training rides at various parks.
I'm picturing mounting the waterer directly to the side of the trailer where I tie the horse.
I emailed the inventor with these questions: Would the plugs hold up at highway speeds to keep the water in the tank and out of the drinking bowl? What are the dimensions of this product? What does it cost?
I'll update this post when I get a response.