Rocosil,
It seems to me there are a lot of older trailers around with very light single-skin and double-skin panels. The loads to be carried in a teardrop are so low that it is the durability of the skins (puncture resistance, for example) that is the limiting factor on skin thickness, not overall strength.
If a single skin of 1/4" ply with a bit of framing is strong enough, why make the structure much more difficult? I'm a great fan of double-skin construction (built many racing yachts that way) but the strength and stiffness isn't really needed for a teardrop.
Just my twopennyworth.
Andrew