Oh boy. I don't even know where to start, so, I'll just start with the instructions for using 8115.
Here's some important excerpts from the 3m 8115 data sheet.
• When the manufacturer’s directions are followed, this product can be used to bond door skins, roof skins, quarter panels and box sides. In addition, product can be used for bumper cover repair under certain conditions. Typical substrates include cold roll steel, aluminum, SMC, and FRP. This product is not intended to bond structural components of a vehicle such pillars, rockers, or frame members. If doubt exists as to whether a particular component is structural, then that component should be welded.
• Quarter Panels: Adhesive should be applied to the lower edge, the wheel opening, the door jamb areas of the quarter, and at the factory seam of the sail panel. 3M suggests that the rear vertical portion of a quarter panel should be welded. It is acceptable to bond the rear vertical portion of a quarter panel, if recommended by the OEM. Additionally, most OEM’s only recommend full panel replacement. Should you perform a belt cut on a sail panel, 3M recommends welding the belt cut to ensure optimal cosmetic appearance. All areas to be welded should be sprayed with 3M™ Weld-Thru II (PN 05917). Do not apply adhesive to these areas.
• Caution: The adhesive is combustible. Keep any MIG welding a minimum of two inches from the adhesive. As with any welding operation, keep the appropriate fire extinguisher within reach, and be alert to any smoke or flame that may be present. Resistance spot welding through uncured adhesive is acceptable.
I attached the rest of the data sheet below. I think it's pretty clear. The 8115 panel bond isn't even recommended by the manufacturer for use on partial quarter replacements. On a unibody, everything is structural, even the quarters. It's supposed to be clamped, not held in place with screws. It's not supposed to be MIG welded,
ever. The whole bit about induction welding only applies to uncured material, and they list a work time of 90 minutes and did all their testing after 7 days. So, a month later that's definitely cured, which means no welding of any kind.
As for the rest of it, fiberglass and metal don't mix. Ever. If you need a short strand fiberglass base under your body filler because it's going to be that thick you're sculpting, not doing body work.
How would I do it? I'd get out the cut off wheel and start over. The panel bond used was the wrong product for the job, and the installation so far goes against pretty much everything 3m says for using 8115. Panel bond has its place, this wasn't it.
