I am working on making a custom 5th wheel tailgate, but I'm not sure if the openig size is a standard size. Can anyone who has one, measure the opening of theirs and let me know? I need the width of the opening at the top of the tailgate, then the width at the bottom, then how far down from the top of the tailgate to the bottom of the opening. You can just list the dimensions in that order, no need for a lengthy reply, unless you have some suggestions. Thanks, Ron...