does anyone know/be able to modify a plastic fuel tank.

the fuel tank under my bm runs the full length of the rear of the car,i am converting to gas and to get a bigger lpg tank in the wheel well i need to mod the plastic tank or have an alloy 1 made up.

if it can be modded,i can keep my original sender and fuel lines.

with it being plastic,surely it can be cut about then plastic welded back together?

anyone any ideas`s please

cheers
dave