I bought a cargo minivan.  The "cargo" portion means that is has no back seats and mounting points on the walls and floors.  When purchased, it had tool chests, shelves, and a cage between the front and rear.  It also meant that my existing roof racks weren't so relevant anymore.  So, I went to the shop and started to think about it.

I came up with all sort of convoluted solutions on how to mount the bars using bolt holes in the floor (but both of them were on one side of the back end) when I noticed some tie-downs.  When they were removed,  there were two bolts sticking out of the sides.  I quickly came figured out a way to use them.

I machined two adapters that screw onto the bolts and go into the ends of an old bar we had around the shop.  It uses the roof rack's existing fork mounts.  The bars inner diameter was 7/8" and we had some 7/8" round stock.  The round stock was turned down a slight bit.  Then was drilled and tapped the end holes and 3/4" hex was cut into the ends using a mill and an indexing head.  You put the adapaters, pictured below, into the end of the bar and then screw them onto the bolts.  Done.

This piece was machined from 1.5" square stock.  It bolts into the floor mounts and is very solid.  Only one bike can fit in the back using this mount but that's ok, most of the time I'll only have one with me.  The hex bolt uses a 1/4" allen wrench, which I don't always have.  My bikes use metric allen wrenches.  So I got an allen wrench just for this and put a small hole in the block for the wrench and that way, I'll never lose it.  The stainless steel fork mount was also made in the shop.  See here for more.

If the edges of the piece look a little screwy, that's because they are.  I was learning to use a radiusing tool on the mill to give it rounded edges and made a few mistakes but now know how to do them.  No need to go back and fix them, just wait until next project and do it right.

This was the final solution looked like. The bar goes across from side to side and can fit 2-3 bikes. The downside of this is that if you want to sleep in the back, the bar isn't very conducive to that. That's why the smaller, single bike mount was made.  It utilizes floor mounted bolt holes, in the front left.