Another rust problem

[DeathBy240SX]

The spot for my rear tire is pretty much rusted beyond repair. It is rusted in the lower area where the spare tire sits and on the hump on the drivers side (the opposite of where your fuel pump is located). I guess I have a few options (since I cant find a rust free shell up here anywhere).

1) Cut out the trunk of a car without rust in the area and get it welded in to fit like stock, and so the stock gas tank will still mount up.

2) Cut the rusted part of the trunk out and weld steel straight across and somehow get the gas tank to mount up to it.

3) Same as above but get a fuel cell.

Any other ideas?

[PeeWee Herman]

I hate to bring up an old thread but did you ever fix the rust? I have a similar problem and am wondering which route to take also.