I’ve now got most of the underseal stripped from under the car, the main problem areas were the wheelarches – the stuff was 1/2 inch thick in places!
As I was suspecting, pulling the underseal off revealed a few areas of rust – Some worse than others:
Apart from the rear sills and the seatbelt mounting (last picture), this was all hidden neatly behind layers of underseal. So either it was there to start with and just sealed over, these were problem areas that weren’t treated properly when the sealing was done.
The fact that the big hole in the wheelarch (Third picture) was covered up on the other side by a patch of fibreglass matting, and the NS sill had a huge lump of filler whacked into it doesn’t fill me with confidence in any previous repairs, though!
On the other hand, that’s pretty much it now – at least as far as the rear is concerned. I don’t think there’s much more hidden anywhere, as I now have a fairly intimate knowledge of the area!
Most of it looks pretty simple to fix, as it’s all in the middle of single layered panels, with no complex curves or angles. Those rear sills are going to be pretty tricky though – there’s three different panels joining in that area, all with different curves and angles. But I’m determined that I can do this myself, it’s just going to be a steep learning curve for me!