I like your tail roller and winch setup. I'm thinking of doing the same with my S280. I'm going to make my tail roller removable though with receiver hitch tubes mounted on each side of the bed. That way I can remove the roller when not needed. I've also got a dump installed so unloading should go easier (just dump it out, with the winch holding it, of course).
I was worried that a 8K winch wouldn't be enough but looks like you're loading a much heavier shelter with a 4,500lb winch. I may still go with a 8K though because I've also got a deuce tanker bed that I'm thinking of putting some skids under so I can winch it up into the bed when needed.
Since I already have the dump installed, moving the bed back would take a whole lot of work so I'm going to mount my winch under the bed and use some rollers to get the line to come out in front of the bed.