Reddit mentions of Plexus MA310 Off-White Two-Part Base & Accelerator (B/A) Methacrylate Adhesive - 50 ml Cartridge - PLEXUS 31500 [PRICE is per CARTRIDGE]

Just read the tube. It's Plexus MA310, which is methylacrylate. It's really expensive, but DAMN is it strong.

https://www.amazon.com/Plexus-Off-White-Two-Part-Accelerator-Methacrylate/dp/B007468O56

The cartridges last a lot longer if kept refrigerated and the easiest way to use it correctly is to squirt it into a ziploc bag, close the bag, zip-tie off the portion with the adhesive in it, then mix the two in the bag for 2 minutes until it gets warm, then use a razor blade to cut a hole in the bag so you can dispense from it.

After you've applied enough adhesive you set the bag aside and use it as a gauge to tell when the adhesive has finished curing.

I've used it to glue aluminum to stainless steel. Delrin to Stainless Steel, PVC to PVC (mostly as a gap filler), and other joints where welding or other adhesives might not bond well.

If I want to joint two shells together I usually make a patch plate of some kind to do the structural work. A little piece of polycarbonate or aluminum and a few screws works great. But to fill in around the seam you want something like this adhesive or an epoxy putty so you can sand the joint back down later.