I have just such a trailer (4' x 8' bed)
The tongue is made of 2 pieces of U channel so that it can fold down on itself, and is held in the trailing position by a simple Linch Pin. If storage height is no problem that feature would be unnecessary.
The bed is made from 2 frames connected to each other just behind the wheels so that the aft end can be flipped over to fold flat on the forward end just like a giant hinge. When in use, 2 machine bolts secure it in place. A length of square tube ~40 cm long is mounted perpendicular to and centred on the side frame behind each fender at the aft end of the forward bed section. When the bed is folded, the whole rig is tipped upright onto casters mounted on the ends of the tubes. (A simple but clever piece of msll angle iron hits and grabs the pavement as the triler is tipped up so that it doesn't skid on the casters but is off the ground when the unit is fully upright. At that point, only the casters support the trailer in the upright position and permit it to be moved around with surprising ease.
I'll post some photos for you later today.
Cheers, Garrett
Self-storing Trailer Photos (Follow-up)
Here is the trailer mentioned in the post above. (Apologies for not having prettied it up for the photos, but it’s about 7 years old and has seen a lot of use.)
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Construction details should be evident, but I’d be happy to answer any questions.
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Cheers, <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:PersonName>Garrett</st1:PersonName>
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<img src=http://members.shaw.ca/glia/Tongue.jpg>
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<img src=http://members.shaw.ca/glia/Side.jpg>
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<img src=http://members.shaw.ca/glia/HInge.jpg>
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<img src=http://members.shaw.ca/glia/vertical.jpg>
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<img src=http://members.shaw.ca/glia/upright.jpg>
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<img src=http://members.shaw.ca/glia/Stop.jpg>
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<img src=http://members.shaw.ca/glia/Sides.jpg>
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I had to make new top rails for the sides a couple of weeks ago. They simply drop into mating the holes in the framing members, and are attached to each other at the inside corners with loose pin hinges for easy removal and installation.