Very cool. I was throwing around the idea of building a greenhouse on a trailer. Of course it would need to be aerodynamic to some degree, and very well built to withstand the winds. I was thinking polycarbonate panels like you did, but with steel studs for the framework. This would save on some weight and allow me to get a little more creative with the shapes.
Would be cool to roll up to a farmers market to sell your veggies directly out of the greenhouse. And if you're one of those people who has to fight shadows for sunlight, you could move it once or twice throughout the day to stay in the sun. Obviously not an idea situation, but some people just cant get all day sun where they live.
http://www.skoolie.net/forums/showthread.php?t=9883 - 7.3L 4x4 Shuttle Bus Toyhauler conversion