Huh, :)the bolt all the way through idea is something I never though of.
I can grab a 1/4 inch bolt from the farm. We have a bunch of them that are that long or longer and we hardly ever use anything that small anymore.
Heck, except for cosmetic reasons I would not really even need the cap anymore. (I would probably keep it though) If the bolt was extra long I would not need a wing nut either. Just paint it black to match the bumper and go.
Thanks Everyone . Sounds like a good project for this weekend when it will be too cold and windy to go camping.