Removal of petrol filler neck and wheel arch welding

[praivo]

Because of the double skin design I can't really get to it from the inside and the petrol filler is in the way on the outside.

What do you mean by "double skin"? I have a hole inside the wheel arch (right above the filler neck and big enough for me to see the inside of the rear lights through it) too and I'm planning on fixing it soon. To me it looks like there's only one layer of metal and removing the plastic trim in the boot and the light should be enough.

The filler neck on my car is held in place by the rubber seal behind the door and one bolt under the car (which rusted and broke off because the mechanic who installed it was an idiot and didn't even grease it, let alone use a stainless one, so it was replaced by a self-tapping screw). And as I found out when the bolt broke off, taking it out will let you pull the neck out of the seal and then out of the wheel arch. I'd probably rest it on the wheel to avoid damaging the hoses that connect it to the tank.