Thanks USMC Vet. I looked at those at a mobility upfitter. Since I am so unsure as to what I am ultimately going to want to carry or tie down, I am trying to cover all my bases. Right now I have a bunk bed cot and motorcycles, but mom's mobility is not good so a wheelchair is in her future and I want her to be able to ride in the wagon. Hince the roof track and a hammock might be fun also. I also serve as the family mover so lots of tie downs are better for me.
Understand your situation better now, and I have a suggestion from out of left field (love baseball). In my Wagon, they installed a "monkey bar system", basically roll bars with added sections and strength, to help me grab on to and assist shifting myself around the wagon. You can see some of it in post #7
of the Thread, "On the Road Again". They run from the front of the drivers compartment to about a foot behind the slider.
Now don't start laughing,
but you could have something like that installed by the up fitter , starting either in front of the slider, or behind it and running to the rear of the Transit. You could hang a lot of items, including a cot above your bikes, from them and then take the cot down to store. There is a company in Phoenix that makes replacement straps for Jeeps (replacing the OEM attachments) to use as hand holds etc that are made out of para-cords with 1000 lb capability for each strap.
Good Luck searching for what will help you best.