I used the existing warped piece that I had (tank side only), card board templates for the curves & edges & a bit of measuring & made a pattern to replace my trunk pieces (bigger though to reach all the way to the edges) & cut the new piece out of 1/4 plywood.
I cut it as 1 piece then cut it apart at the seam so the seam & the grain all line up then finished it w/ left over deck stain on both sides.
I used the original brace under the permanent piece & bent up some Z-clips out of sheet metal so the removable piece supports on the other in the middle kinda like the original.
