Went to a fiberglass form fit after trying to figure out how to adapt any of the six seats i have on the shelf. Either they would could not be adapted or just wouldn't fit.
Pan in raw state - from top
Bottom view. Where it formed to the frame and seat area can be seen.
Put an old router and router table to work for the trimming.
The plastic is left from when the entire area was covered while laying the fiberglass. The trimmed pan fits like a glove. Missed a bubble when laying the matts but will be of no effect.
Pan padded and wrapped. Not the best but it is functional and fits.