'69 C20 Fuel Tank Change Options

[chevyremod]

I believe I've read every thread about removing the interior tank and replacing it with a location to the rear of the cab.
It appears that 3rd party manufacturers only make tanks that fit in the spot of the spare tire.
I would like to change to a tank that fits under the bed, maybe inside the bed wall, just to the rear of the cab. I've seen pictures of trucks with a fill tube coming into the side of the truck bed so I feel like there was an option for a second tank that was located in this area. However, I've been unable to locate a tank that I'm able to purchase that fits in such a location. I suppose this is because it's more danger for a tank to be located outside the frame. However, I'm going to do the work myself and I've seen the attached pictures of '73 tanks that appear to fit the bill.

So, have any of y'all acquired any tanks that you were able to place in the location I'm asking about. If yes, please include pictures and build threads, if any.