[DanEC]

I would suggest removing it to work on the underneath. ERA provides a black felt liner material for covering the exposed hand laid fiberglass on their trunks. A lot of us smooth it out with sanding and filler and paint it instead. This can be done on a finished car but just have to take a lot of care to protect the paint.

I think a few may have also rolled and fit an aluminum sheet to cover bare fiberglass and slide behind the overhanging lip for the perimeter frame.