[DanEC]

I'm not an expert but typically a hand laid up body is considered structurally stronger than a chopper gun body - all other things being equal. Then it gets into the resin they use, how thick they lay the fiberglass, the experience and technique of the fiberglass workers, etc. Some of the better manufacturer's will advertise they use a higher quality, high temperature - low shrinkage resin. I've been hearing lately that the SMC resin is far superior to the old polyester resin on fiberglass mat but I haven't seen that being advertised that I can recall. They typically use fiberglass mat which is the random strand mat since it doesn't imprint on to the surface like the fiberglass cloth that looks like cloth. Coremat is a thick mat material (say 3/16 inch thick or so) that is sometimes applied on the underside of fender tops to prevent stone and rock damage if kicked up. Thickness of fiberglass can be an indicatior of quality but also adds weight. I would not want to see anything less than 3/16 inch thick in general. Some areas go up to 1/4 inch for strength. If you see any areas in the 1/8 inch range that is getting pretty thin. All manufactuer's that I'm aware of use gelcoat in the mold before applying fiberglass and the thickness of gelcoat is an indicator of quality. It needs to be thick enough that you can rough sand the body for glazing and filler and leave plenty of gelcoat thickness to keep the fiberglass sealed and stable. And then the molds, or quality of the molds is a huge issue. The straightness of the molds and their setup and preparation for use have a huge impact on quality. Good molds and mold preparation should result in flush panels and very thin mold separation lines in the finished body. I'm working on an ERA and a couple of things I appreciate about their body are the thickened edges around the cockpit so I can roll them to mimick the original. Also, they make extensive use of interior fiberglass panels, or double panel construction for attaching hinges, hangers, and aluminum panels too. They sandwich metal plates in between the door inner and outer skin to carry the hinge and latch loads. They also roll under the rocker panel area similar to the originals. About all I can think of for now.