Go to: www.autobodystore.com. It is hosted by Len Stuart. Scroll down to the bulletin board. Post your subject and question.
Within a few days or sooner, Len will answer your question with a full explanation. He and other experts that use the bodystore forum always know what they are talking about, as you may get answers from other paint and body mech's.
They know fiberglas, urethane, paint, and anything else your would need to know about your metal or fiber glas car.
They also know framework, and all mechanics. There is not any solicitation's to purchase any products.
