[strictlypersonl]

There are a dozen good ways to make a fiberglass body and fifty ways to f**k it up.
The basic body shape must be correct and the doors, hood and trunk lid must fit their openings. Some shape errors and panel mis-matches cannot be easily fixed.
Strength is usually not an issue unless the body is not well supported.
You can lose a little weight with the right materials, but you have to watch for distortion and cloth weave printing through the paint.
Good inner-panel support can make a light, stable body without exotic materials.