|Half-moon lay down tank|
Nah, we're not suggesting skinny dipping in the nearby creek. But horse loving folks who travel with their four-legged pals know that sometimes there's not enough water in their horse trailer for themselves and their equine friends. Enter auxiliary water tanks for horse folks.
These tanks are designed for the horse crowd: Some "double" as saddle racks, others are designed to ride in the back of a pickup truck, squeezed in between the sidewall of the truck and the trailer gooseneck. Since few of us have goosenecks (and more likely have fifth wheel hitches) they don't always cross over as well as some. Still, if you pull a travel trailer, the "48 gallon half-moon lay down" tank might work out for you.
|18 gallon "slant" tank|
The ones of real interest are designed for inside a horse trailer, tucked away in a corner or in a dead space area. Ranging from sizes that contain as little as 18 gallons or as much as 39, they stand upright (requiring some work at tying them in place) and can give you that extra edge when needed for more water.
How could you plumb such a critter? All of them come with hose spigots, allowing you to "gravity flow" your water where needed. Add an auxiliary 12-volt RV water pump, you can easily transfer your extra water into the existing house system through the normal fill port. Get even more fancy and you could run a permanent water line from the horse tank to the water line heading into your RV's water pump inlet line.
Before you start your installation though, keep in mind the weight of the tanks plus that of the extra water. Don't overload your RV's weight carrying capacity, and don't place a tank where the extra weight may adversely affect load balance and road handling.
Here's a link to horseloversoutlet, a retailer of horse water tanks systems.