[Dan in Pasadena]

It doesn't seem like moving the crossmember would be THAT big an issue with a street truck like ours that is unlikely to carry much; if any significant load. I don't think I'd be too worried about that.

If the tank bolted to the upper flange without additional support, it'll bolt to the bottom flange with no structural concern. So you're suggesting surround the tank just for collision protection?

I'm thinking Rudy bolted it as he did - on top of a square tube spacer - to increase the ground clearance. Plus, MAYBE(?) that spacer serves to allow the tank to be removed from below if you can take that spacer out?

What I like about his installation is you can buy. New mustang tank for less than $100 brand new. That makes welding it doable. I'd never try welding on a used tank, full of water or otherwise.