I don't have mine in yet (it's sitting on the workbench waiting for spring) but I have an 8 gallon tank that I'm mounting under the bed on the passenger side. Should be out of sight, with no loss of ground clearance, and am working on a sweet hideaway solution to fill it. If this thread is still active when I get it in, I'll post pics.
US Plastic is where I got my tank. There's a TON of options out there, I started finding more once you just start searching for a "polyethylene" tank rather than a "methanol" tank. Cross-linked polyethylene is what almost everybody makes their tanks out of, and is perfect for methanol....mixed or straight. If you don't need the impact strength and rigidity that the cross linked gets you, just standard polyethylene will work just fine.