Up front, let me just say I haven't done a water test, but the repair seems very sturdy. That being said...
I cut a final set of gussets and shims out of LDPE. You can see the outer diameter of the fitting inside the tank is much smaller that the diameter outside. The shims go under the flange to provide the proper angle between the tank skin and the fitting (or what I perceive as the proper angle). There's no way to tell unless I drop the tank. The gussets are 1/4" thick, so there is plenty of height, even with the shims in place, to get a good glue joint to the edge of the flange.
I did note yesterday that in taking the fresh tank out of the Safari, the top was not flat, but drooped. That may be the case here, which means the top skin would come back up "flat" once the tank is full. But that's water over the dam, as they day.
The white in the lower left portion of the clamp photo is a stiff piece of paper on the face of the ceramic heater. I applied heat locally for about 3 hours. When I look at the photos, it makes me think "that inner gusset can be inserted from the top?" Yep. Just use several pairs of surgical gloves to keep the very Nasty smelling Scotch Weld off the skin. I think I had 25% of the glue on the gloves...
If this worked, the Sovereign
is back in business!
BTW, if you decide on using Scotch Weld, get plenty of the 10:1 mixing nozzles. I bought six and with all the testing and self-doubt, I used 4 to get to this point. I wish I had bought 10. (If you're careful, you can re-cap the glue after using only a small amount from the dispenser, so the mixing nozzles seem to be the limiting factor in getting the most out of a $30 tube of glue.)