I was at a local VW shop yesterday where there was a 64 Karman Ghia having it's rusted out floor pans replaced. Same technique for removal of the old pans (drill out old welds), same problems in replacement metal (single good source and expensive), same procedure for welding in the new pan (wire weld small holes and grind), same situation for putting the seat base back in (the same welding technique) everything was the same, and it looked good.
Jim