The GRP lids have molded foam insulation with built-in chickenwire reinforcement. Remove at your peril, it should be fire retardant. Better to fix some thin foil faced foam inside the van, then it can't come unstuck and drop onto the engine
1985 Oettinger 3.2 Caravelle RHD syncro twin slider. SA Microbus bumpers, duplex winch system, ARC 7X15 period alloys