None from the factory that I am aware of, can't say for certain. My 64 Chevy had two under bed mounted tanks that mounted on the side of the frame in between the cab and wheel. Kinda like the 70's chevys, but I think those were aftermarket. Anyhow, I don't see a legal issue at all. However I would recommend covering it somehow as a full fuel tank in direct sunlight can creat enough heat to cause some issues. There are many rear frame mount tanks on the web. I would look into those and find one that doesn't hang as low.