Finally; it occured to me recently that I had a can of washers for plumbing, and they might fit a mod and it turns out 18mm = 0.7 inches which is just a little smaller than 3/4 in, so 3.4 inch washers work pretty snug;
a 6 inch bolt - 3/16 inch, and a few plumbing washers, and that goes up into the tube mod back end;
just threw that together.
I'll have to make refinements to ensure it holds and makes firm consistent eletrical contact, and wrap it up etc, but it works; been vaping on that the last couple hours.
Power is Radio Shack universal ac to dc adapter set to 7.5 volts
The thing on the lower right is where it plugs in / unplugs to the cable from the ac/dc power adapter.