My buddy has a 71 Chevy Vega. There is a plastic panel on the back lower valance area. It of course is about 1/8 thick and has numerous cracks we need to repair.

We are using some of those metal hot staples across the cracks to reinforce them.
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I have some JB Weld Plastic bonding adhesive, a 2 part product.

I also have some short hair evercoat filler I will put on the visual side.

My question is, what is the best to reinforce the back side of a plastic repair, the JB Weld or just short hair bondo?