I think when we spoke via Reddit you said you were going to use Sikoflex 291 – since then I’ve had a few suggestions of Sikoflex 292 because it has twice she sheer strength on 291. I also had a suggestion of bitumen which is a sealant that is sometimes used in roofing which can be used in tempeatures of -20°C to 80°C. For now I would stick with the Sikaflex but if I find anything else I’ll keep you posted.
Good luck!