Hey guys, I learned how to do this somewhere in this thread but I don't know if anyone's made a concise post about it yet.
I was successful soldering in a 2" triclamp ferrule
into the side of a keggle. I first drilled a 1 7/8" hole with a hole saw from the hardware store, and then flared it out with a custom tool I made on the lathe:
(It's a 15degree taper from 1.75" to 2.020")
I pulled that through with a 1/2-20 grade 8 bolt/nut with a 2" PVC coupler for the outside. Don't discount the importance of a) the fine thread bolt and b) the grade 8 hardware because it takes surprising force to make the dimple.
Once the dimple was formed I tapped in the 2" triclover nipple and soldered with stainless flux from McMaster and standard lead free solder from Menards:
I then used the element adapter kit from StillDragon
to complete the install of your standard Camco element.
This approach makes it really easy to take the element out for cleaning, and also avoids the issue of threading an NPS element into a 1" NPT coupler.
I hope this helps someone out there!