I was toying with this concept too. I wanted to take it on a solo hunting trip instead of the van. I would be camping in it for up to a week so it had to provide some level of sleeping comfort.
First I removed the back seat (took about 5 minutes). I slid the front seats all the way forward and had just about 6' of length in there to sleep. I am 6' tall. I started to design a storage box to fit behind the front seats that would be the same height as the rear cargo floor. The problem was that I still wouldn't have much room for my gear. It also looked like the box may interfere with the front seat if not designed right.
Then I noticed the front seats fold almost flat without the rear ones in there. I tried it out for sleeping and it wasn't bad. Like sleeping in a lazy-boy recliner.
Anyway that was as far as I got with it all. I ended up just taking the van since it was all set to go.
But I kept the back seats out out of the Tracker and it makes it way more useful for me that way. Still thinking about designing a storage/bed thing for it someday.