Now it's time to turn to the trunk lid itself, as it needs a lip around the edge to be rigid enough to maintain body curvature. A lot of the foam and some of the plywood remained attached to the trunk lid when it was pried from the body buck, so new foam was needed for those areas where the foam was ripped away or damaged. I cut existing foam and spaced the new foam 1/2 inch from the trunk lid edge so the lip could be built from a combination of fiberglass and body filler. The lip thickness is needed to add rigidity to the trunk lid so it will keep shape during later mold-making.
I use stitch-matte cloth, which is a two-ply matte/cloth to quickly lay-up the fiberglass portion of the edge. This material is stiff enough to stand up straight during lay-up, but flexible enough to curve with the trunk lid. Once cured, the fiberglass lip is cut off to remove sharp protrusions and sanded to remove the top waxy layer. Body filler is then applied to form a rigid edge. I use body filler on the outer edge as it's easier to sand and shape than fiberglass. After sanding with a long board, the trunk lid edges are straight and the trunk lid fits the opening.
Well, one more body feature is now present on the GTO body plug. I thought about cutting out the rear window opening, but it is better to leave it in place until a mold is made on this plug-but back to the question of trunk or boot. I'm guessing if you spent your adolescent years in Europe or a British colony then it's probably natural to call it a boot. I've owned British cars most of my adult life, and I still don't find it natural to call the rear luggage compartment a boot. Given that explanation, if you've come to the conclusion I'm just an American guy who loves European cars, you're right.