I think I paid around $25 each for those holders. The beauty is how adjustable they are, up and down, side to side and they each have a twist lock so they can't slip out.

If you don't want the expense of the fancy holders you could still use my cross member idea and secure your tube idea to it. By using the angle across the full width of the stern you could probably add 8 holders. If your buddy doesn't have a deck mount in the area you want to mount it all he has to do is buy a quality stainless steel deck hinge mount and put one on each side where it will best work to secure the "rod rack" and you're in business.

It is super easy to put on and off and like I said, when you remove it, you never knew it was there.