I was going to blatantly copy the Prinsu. I wanted a flat low profile. With the T-Slot, I can add and remove mounts and tie downs as needed. I drew it all up then found one for sale for less then it was going to cost to build. I didn't end up building it for my 80. I have however built several "basket" type racks for my other vehicles over the years.
What you need to do is, look at what's out there and figure out what you need. My basket racks worked well but now that I have a flat rack that's modular, I will only use that type now. Using tubing, you can accomplish the same. Just add in mounting points.
I just got back from a trip, I'll grab some pictures while im cleaning up.