Re: A step-thru china girl. Almost.
Nylon locking nuts will prevent loosening due to vibration. But imho, I would not reinforce a frame with clamps. Even very tight clamps can slip with enough load. I would weld gussets onto the frame to reinforce it. And if those clamps are not made out of very hard steel, they can also bend very easily, which will eventually cause them to loosen. Weld some gussets on it and git-r-done.