You can use a larger disc to grind that interior. But man... I bet you are putting too much weight on that spoiler
But nice work you've done, try to fab a mold out of it (when done) and refab the trunk from scratch using the mold and fiberglass
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Danny
1994 Silver SVX in hybernation, awaiting for the
monsterous awakening (Lebanon)
1967 Mercedes-Benz 250SL Euro Specs, Hard/Softtop, White/Red. Under Complete Restoration
2013 Mercedes-Benz SL350 Euro Specs, White/Red. Mint... Another step into SL Collection.