Ed,for a pop up version of any of the trailers these guys have drawn up, I need to know what materials you had in mind. Work with what is comfortable for you. If sheetmetal, we could make the top section out of EMT and skin and insulate it for example. As small as that trailer is, the roof is in range of "crouch into it, lift up roof by standing up" with no mechanisms. I can design a simple toggle that you pre-set, once the roof is high enough the toggle falls into place at each corner and you let it back down.
To reverse the process, you re-position the weight on the toggle. Lift up and it unlatches for you, let roof down.
Hang the door on the roof section, opening out. After lift, install a 2' door section on the bottom to fill that hole, done.
It opens up those aero designs like jacobnev's or sven7's (very nice) and lets you build low and live high. Both of those designs have that 2' section of straight side for the slip.
If building for cold weather, you need at least a 2" wall insulation. making it pop up will reduce interior width 4.5", 2" each side plus .25" for clearance. Small price to pay for stand up comfort.
Use sliders made from UHMW plastic strips at the corners, installed with countersunk rivets. This stuff is very very slick and tough, and will prevent binding.
My material of choice is a XPS foam core covered with very thin veneer inside and out, layer of glass/epoxy, and finish with linear poly. That may not be in your comfort zone but it is what the really light and fast boat builders would do.
Edit 1: I would build the trailer out over the wheels, as close to the Tow vehicle width as possible. Add a center divider over the hitch tongue to keep the crosswinds from crossing over the gap. aerohead has these ideas around here somewhere and explains them well.
The XPS/veneer/epoxy/glass sandwich weighs in at 0.6 lbs per foot at 2" thickness. take off 0.08 lbs at 1.5" thickness.
5'x11' plus 2' side is about 120 feet. it would weigh in at 70~80 lbs.
Use the bluecor .25 foam and build it up, making radii as you lay it up. each layer bonded into a radius gets stronger and stronger, think motorcycle helmet.
http://building.dow.com/na/en/produc...on/bluecor.htm