The factory uses Henry's Roof and Gutter sealant, but that's not available in the US. I guess they are close enough to the Canadian boarder that that's what they import.
The US equivilent is Hengs 311 or NuFlex 311 - both seem to suddenly not be available on Amazon after being there for years. Now, I find it only at campingworld.com. ProFlex is also commonly suggested and used.
I've used Manus-Bond 75-AM but it was difficult to use and non-self leveling. The difficult part was it was super sticky and seemed to magically get on everything within a 10' radius of the area I was working in.
Here's a link to the Camping World listing of NuFlex 311:
https://www.campingworld.com/heng%27...ite-52125.html
PS. I agree DO NOT USE DICOR. Some are using Sikaflex which is a great brand and very popular for boating. But they come in dozens of "flavors" and I'm not sure which one is appropriate.