Always glad to hear people get use out of a writeup.
Unfortunately I think you might find the HF cargo is going to be too wide to slide out of the back of the X. Assembled as intended to go into a receiver it's about 53 1/4" wide. You could assemble it without the 2" square tube, but I don't think it will clear even like that.
Thanks for posting it up, kind of the reason I went ahead and opened this thread in case anyone wanted to get some ideas. The discussion has been helpful in working out some details as well.
I probably described my intentions wrong, I woulden't intend for the HF rack to move. I am intending to assemble it without the 2" tube though, and try to offset it to the passenger side to see if I can still fit tall slim items in the drivers side like I was mentioning about my cot and camp table.
Right now I'm thinking of putting it on legs and making tabs off the slide rail mounts to bolt it to. I would like it to be kinda removable though, woulden't need to be quick but undo some bolts and set it out kind of deal.