Springs for a solo seat

I am putting copper bobber springs on my solo seat on my XJ 700. After looking all over the Internet it still isn't clear exactly how they should be installed. Can someone give me peace of mind?

I have welded studs to my seat pan so that with a fat washer and a locking nut the top of the springs can be fastened. The mounting bungs that came with the springs are made to be welded to the cross beam, but how do the springs attach to the bung when it is not threaded to accept a locking nut? I have seen a few places suggesting to slip the spring over the bung shaft and use a cotter pin. Should I really believe that a small cotter pin is all that is in the way of my seat bouncing off of the bung shaft.

What is the proper way to mount these springs?

 

When I did my seat, I made the pan out of aluminum, so the springs were just screwed into the seat pan with real short sheet metal screws with washers on them.
For the bottom, I used 1/2" rubber bushings, screwed to the frame cross member, so the springs just sat on the rubber bushings.
I didn't want to weld anything on the cross member at the time, because I didn't know if I would be happy with the spring seat or not. I've since replaced my spring seat with one from a Sportster, which I like alot better.