Technical 41-48 tank ideas

I was flipping through the custom car chronical the other day and came across a European fellas 41 Ford build. In this car he cut out the trunk floor and mounted a gas tank to the trunk floor.
Seeing how I don't have much for a trunk floor I thought this would be a good solution. I was looking at some more modern tanks Mustangs Camaros etc, and width wise they're a great fit, but I only have 18"-19" heightwise and these tanks tend to be 22"plus.
Does anyone have any tank suggestions or is aftermarket going to be a better solution?

 

Tanks Inc. makes a direct replacement for ‘41-‘48. $299.