Any adhesive used should be one that maintains a level of inherent flexibility to withstand the rigors of a high shock environment like automobiles and to compensate the expansion and contraction of the parts adhered together. Some epoxies either have this property or can be mixed to impart this property when cured. Auto manufacturers use quite an array of adhesives now; something like a panel adhesive or a seam sealer would likely fit the bill. I’ve used a 3M seam sealer that is quite thick which comes in a plastic sausage wrap to be applied from their gun which would work well I’d bet, although it’s about $25 a sausage. That’s why it is hard to beat the Liquid Nails/ PL200 at $3-4 a14 oz. caulking cartridge. If you’ve ever had to disassemble something assembled with stuff like this you would have no doubt about its suitability to hold stuff together. Good Luck!