a8, Looks Great! Good job resisting the temptation to bring the back down to the top of the tailgate.
Have you considered just making it to where you crawl in, and just lift it up, to make it "Pop". I mean, for all the time, money & effort you'll put into cranks, guides & pulleys & such with the risk that it may take 2 or more tries to make it work, and the system will take up valuable space.
You could just make it where you lift it manually on 1 side, then prop it up or fasten it in place, then go lift the other side. That way you're only lifting half the weight at a time while the other side remains attached and controlled. There may be a way to do it where you just stand on the outside, beside the truck, and lift too. You'd just want to be sure to engineer it such that it has the clearances to "Unpack", but I'm sure you'd account for that.
I was considering doing something very similar a few months back and that's what I was going to do, and mine was going to weigh more. Your light construction method using fiberglass should make it a cinch. Something to think about anyhow.
Again, Great JOB!!
