Hi James,
Nice to have met you at Hessisch.
A little tip for removing the underseal from your inner wing panels that I used was to heat a small area at a time with a heat gun. This softens the underseal making it easier to scrape off. If you want the panel really clean, heat it again, and spray white spirit on,the remainder of the underseal should run off. It's very messy, but I think you'll find it quicker.
My car came from Sweden, and it was caked in the stuff! An afternoon on each inner wing, and the job was done!
Best wishes,
Gavin.