So, to recap - if you take a mold from a part and the mold shrinks as it cures, the mold will be smaller than the pattern part (the one you're trying to copy).
If the resin you make the part from shrinks, the part you make from the already smaller mold will be even smaller.
Both of these factors are very, very, very small, but if you're trying to build a car and want to maintain tight, even, parallel gaps, even a single mm is going to wreak havoc.
So I decided it would be easier for me to add a small amount to the pattern part, rather than having to add dimensionally to the carbon part which isn't really easy to do. Then the parts can be fit to the car.
Singer does this (at least with their "classic" model) - the carbon body panels are made with intentionally small gaps which are then fit by hand to the individual chassis.
I did a bit of testing and figured out a way to add a 1mm strip to the edge of the decklid on three sides:
And went through the surface coat spraying and block sanding process again, and again, until it was perfect...again!
And finally made a mold, again!
