Well, like anything else, find the center of gravity and she'll go. The guys over at rcFoamFighters.com did a great build along on the "bullet proof wing" that i bet would apply to your platform perfectly.
You've probably finished this by now but here are my suggestions:
Plastic iron on covering would probably need to be of the "low temperature" type. You might be able to get away with nothing more than packing tape. If you really wanted to spend some time and money, you could use 0.5 or 0.75 ounce glass cloth applied with either epoxy or water-based polyurethane. Of course, the fiberglass will add weight
I really like the overall design. Did you use any washout at the wingtips? What airfoil(s) did you use for the root and tip? What's the span and wing area? I've been thinking of building something like this as well. Looking forward to seeing more pictures.