Aftermarket fuel tank fitment issues in the truck...does anything go right for us?

 Last year, I forked out around $450 off ebay for this 1948-60 Ford Pick Up Fuel Tank 65L Under Tray Chassis F1 F100 Truck Pickup 

It looked the goods and seemed nicely tig welded. The thing is: how the hell do you mount this thing?

In other words...where it is supposed to sit? I have had a couple of looks on YouTube but have yet to be convinced that how I have mounted it is actually gonna work? I have seen some people mount them from underneath, but I don't like the idea of having the brackets support the weight, rather, I want them being supported on top of a chassis rail. In yet other words, this is what I have so far come up with...

At least I can get a nut on the bolt from underneath. But of course the tank sits up quite high. That can't possibly work?

It sits flush. But it did take a little bit of grinding of the rail. Not much. About 1mm.

It looks good here. I tried flipping it around but the mounts were around the wrong way. That is, they are staggered to suit the slight drop in the rails. If I turn the tank the other way, I'd need spacers to compensate. 

However, all this is possibly irrelevant, as I am not sure this is gonna clear the wood when I install it.

The only consideration is: the tub actually does not sit on the chassis. It is elevated on a set of rails. So, there is a possibility the tank will clear the wood. See below.

Whether I have enough height is an issue. I suppose the right way is to mount the tank on the next chassis rail. That would eliminate height issues, but how the hell do you bolt the thing in?

The only way to do it is to drill holes in the lower rail, weld nuts and then lift the tank from underneath and bolt it through the mounts and onto the chassis.

Like this example: