Would you look at that! I've been reading about builds on this site for over a year in preparation of the day I would be able to acquire a trailer. I was just recently able to do so! It's a 4x6 with a 4ft tall wooden box that the owner built. It's small, but the price was right. My plan was to modify it as cheaply as possible to sleep four. Interestingly enough, I finally settled on a design that is almost exactly like yours. Funny thing is I never saw your build until today when i was perusing the lift-top build thread ([url]viewtopic.php?f=5&t=50969[/url]) looking for ideas on lifting and supporting the outer shell. Because I plan on a loft for the kids, I planned on our bed being much closer to floor level, but the double slide-out along with the outer pop-up is exactly what I was going to do!
Due to the bed being lower, I can't use the slide-outs for supporting the outer shell. Instead, I plan on attaching square tubing to the trailer frame that will slide inside the front corners and near the back of the outer shell and I will use a metal pin on each tube to hold up the top (the loft bed will be part of the bottom structure). I plan on manually lifting the top (with help) at the moment, but a hand-crank winch and some pulleys are on my wishlist.
I've already started my build, but not the build thread. I'll give you inspiration credit when I get the build thread up, but I wanted to take a moment to say well done (on both versions) and thank you for sharing. Looks like you're not around much anymore, which is too bad because I'd love to pick your brains on constructing and sealing up the slide outs.

Z