passenger side fuel tank

I am looking for a passenger under seat fuel tank - entirely separate from the drivers side tank - veg fuel project - planned on installing it's own fuel filler on the outside. On the normal tank the spout points the wrong way so I could either buy a standard tank, make a new hole and move the spout with a spot of welding or buy an ali tank to my design - are they really £350 ish.
Wondered if anyone has any other thoughts ..
Many thanks

Wouldn`t it be easier to buy a drivers side under seat tank for a military series ? It should fit under the passenger seat (my 109 had twin under seat tanks) and fills from the top. You would take the seat cushion off and refuel through the open door, sounds wacky but you learn to be careful.

as above ,and saves butchering body work need to get tank outrigger as well

Would be easier and thanks for the suggestions.....