the magnet is too deep, and the trunk wont open (or close) witht he spekaers there, or else the speakers themselves just hit the springs.

Make a wooden spacer that goes between the grille and the rear deck. Make it to same size as the grille, so you can fasten the grille to the wood, the speaker to the wood, and the wood to the rear deck

or if you have enough room, just a small spacer that mounts between the speaker and the metal. If you have the clearance, I'd do this.