Sheet metal for rear wheel wells on W126 300SD

[deniss]

I got some really bad news for my car -- the rear wheel arch on the driver side appears to be considerably rust-perforated, and the water has been getting into the cabin from under the back seat as a result.

I don't know the full extent of the problem, but I believe it to be serious enough that I'm afraid to strip the wheel arch with a wire wheel right now -- not sure how much will be left. To add to this, this car is my daily driver, I don't have a garage (live in an apartment complex), and I don't have welding equipment (and don't know how to weld, only know how to solder... ha!) that will probably be necessary to address the problem.

The thought has crossed my mind -- given my situation -- that I could use the POR-15 system and build up the wheel arches by plastering it with the fiberglass mesh painted with the special POR-15 paint that hardens like a rock and then reinforcing it with putty to build up strength (I used POR-15 for some trunk rust repair and have been very happy with the product). I realize that the serious way to address the rust problem on the wheel arches would be to weld, but since the wheel arch is a superficial structure and does not function as structural support for the vehicle, I suppose there's no crime in using something like POR-15 to dodge the bullet. Of course if the problem extends to the frame tubes, that would be a whole different matter, I realize, but right now wheel wells are a problem that needs to be addressed first, or it will lead to other problems without a doubt.

Are the rear wheel wells on the W126 welded onto the body/frame or bolted on somehow like the front fenders? I've assumed they are not bolt-ons. So IF I could find a way to weld to the wheel arch, how would one go about fabricating sheet metal to repair the wheel wells -- what thickness would it have to be and would they need to be welded on in long strips?

This seems to be a daunting task, and given my limited access to resources, I'm not sure how to proceed. The POR-15 would of course be the most accessible route for me, given the circumstances. But I'd also like to weigh my options in regards to getting sheet metal for the wheel arches.

[deniss]

Would also appreciate any input on what would be the suitable and most economic welding equipment for this type of a repair. I've been reading folks say "MIG welders"... I don't have a garage, so portability and working outdoors will be two factors in the consideration -- would a budget gasless flux-core welder with wire feeder do the job?