You could maybe try searching. There’s like a googly thingie you can do, I’m told.
https://www.frontrunneroutfitters.com/en/us/front-runner-footwell-water-tank.html
That bladder thingie is pretty cool! I've been eyeballing this for a while. I currently have several 5 & 7 gallon water containers (Scepter & Reliance) that go on the roof or inside or wherever. It's worked well enough for me...